diff --git a/cmd-list-panes.c b/cmd-list-panes.c
index a131053e..723c7039 100644
--- a/cmd-list-panes.c
+++ b/cmd-list-panes.c
@@ -28,15 +28,16 @@
 
 int	cmd_list_panes_exec(struct cmd *, struct cmd_ctx *);
 
-void	cmd_list_panes_server(struct cmd_ctx *);
-void	cmd_list_panes_session(struct session *, struct cmd_ctx *, int);
-void	cmd_list_panes_window(
+void	cmd_list_panes_server(struct cmd *, struct cmd_ctx *);
+void	cmd_list_panes_session(
+	    struct cmd *, struct session *, struct cmd_ctx *, int);
+void	cmd_list_panes_window(struct cmd *,
 	    struct session *, struct winlink *, struct cmd_ctx *, int);
 
 const struct cmd_entry cmd_list_panes_entry = {
 	"list-panes", "lsp",
-	"ast:", 0, 0,
-	"[-as] [-t target]",
+	"asF:t:", 0, 0,
+	"[-as] [-F format] [-t target]",
 	0,
 	NULL,
 	NULL,
@@ -51,87 +52,92 @@ cmd_list_panes_exec(struct cmd *self, struct cmd_ctx *ctx)
 	struct winlink	*wl;
 
 	if (args_has(args, 'a'))
-		cmd_list_panes_server(ctx);
+		cmd_list_panes_server(self, ctx);
 	else if (args_has(args, 's')) {
 		s = cmd_find_session(ctx, args_get(args, 't'), 0);
 		if (s == NULL)
 			return (-1);
-		cmd_list_panes_session(s, ctx, 1);
+		cmd_list_panes_session(self, s, ctx, 1);
 	} else {
 		wl = cmd_find_window(ctx, args_get(args, 't'), &s);
 		if (wl == NULL)
 			return (-1);
-		cmd_list_panes_window(s, wl, ctx, 0);
+		cmd_list_panes_window(self, s, wl, ctx, 0);
 	}
 
 	return (0);
 }
 
 void
-cmd_list_panes_server(struct cmd_ctx *ctx)
+cmd_list_panes_server(struct cmd *self, struct cmd_ctx *ctx)
 {
 	struct session	*s;
 
 	RB_FOREACH(s, sessions, &sessions)
-		cmd_list_panes_session(s, ctx, 2);
+		cmd_list_panes_session(self, s, ctx, 2);
 }
 
 void
-cmd_list_panes_session(struct session *s, struct cmd_ctx *ctx, int type)
+cmd_list_panes_session(
+    struct cmd *self, struct session *s, struct cmd_ctx *ctx, int type)
 {
 	struct winlink	*wl;
 
 	RB_FOREACH(wl, winlinks, &s->windows)
-		cmd_list_panes_window(s, wl, ctx, type);
+		cmd_list_panes_window(self, s, wl, ctx, type);
 }
 
 void
-cmd_list_panes_window(
+cmd_list_panes_window(struct cmd *self,
     struct session *s, struct winlink *wl, struct cmd_ctx *ctx, int type)
 {
+	struct args		*args = self->args;
 	struct window_pane	*wp;
-	struct grid		*gd;
-	struct grid_line	*gl;
-	u_int			 i, n;
-	unsigned long long	 size;
+	u_int			 n;
+	struct format_tree	*ft;
+	const char		*template;
+	char			*line;
+
+	template = args_get(args, 'F');
+	if (template == NULL) {
+		switch (type) {
+		case 0:
+			template = "#{line}: "
+			    "[#{pane_width}x#{pane_height}] [history "
+			    "#{history_size}/#{history_limit}, "
+			    "#{history_bytes} bytes] #{pane_id}"
+			    "#{?pane_active, (active),}#{?pane_dead, (dead),}";
+			break;
+		case 1:
+			template = "#{window_index}.#{line}: "
+			    "[#{pane_width}x#{pane_height}] [history "
+			    "#{history_size}/#{history_limit}, "
+			    "#{history_bytes} bytes] #{pane_id}"
+			    "#{?pane_active, (active),}#{?pane_dead, (dead),}";
+			break;
+		case 2:
+			template = "#{session_name}:#{window_index}.#{line}: "
+			    "[#{pane_width}x#{pane_height}] [history "
+			    "#{history_size}/#{history_limit}, "
+			    "#{history_bytes} bytes] #{pane_id}"
+			    "#{?pane_active, (active),}#{?pane_dead, (dead),}";
+			break;
+		}
+	}
 
 	n = 0;
 	TAILQ_FOREACH(wp, &wl->window->panes, entry) {
-		gd = wp->base.grid;
+		ft = format_create();
+		format_add(ft, "line", "%u", n);
+		format_session(ft, s);
+		format_winlink(ft, s, wl);
+		format_window_pane(ft, wp);
 
-		size = 0;
-		for (i = 0; i < gd->hsize; i++) {
-			gl = &gd->linedata[i];
-			size += gl->cellsize * sizeof *gl->celldata;
-			size += gl->utf8size * sizeof *gl->utf8data;
-		}
-		size += gd->hsize * sizeof *gd->linedata;
+		line = format_expand(ft, template);
+		ctx->print(ctx, "%s", line);
+		xfree(line);
 
-		switch (type) {
-		case 0:
-			ctx->print(ctx,
-			    "%u: [%ux%u] [history %u/%u, %llu bytes] %%%u%s%s",
-			    n, wp->sx, wp->sy, gd->hsize, gd->hlimit, size,
-			    wp->id, wp == wp->window->active ? " (active)" : "",
-			    wp->fd == -1 ? " (dead)" : "");
-			break;
-		case 1:
-			ctx->print(ctx,
-			    "%d.%u: [%ux%u] [history %u/%u, %llu bytes] "
-			    "%%%u%s%s", wl->idx,
-			    n, wp->sx, wp->sy, gd->hsize, gd->hlimit, size,
-			    wp->id, wp == wp->window->active ? " (active)" : "",
-			    wp->fd == -1 ? " (dead)" : "");
-			break;
-		case 2:
-			ctx->print(ctx,
-			    "%s:%d.%u: [%ux%u] [history %u/%u, %llu bytes] "
-			    "%%%u%s%s", s->name, wl->idx,
-			    n, wp->sx, wp->sy, gd->hsize, gd->hlimit, size,
-			    wp->id, wp == wp->window->active ? " (active)" : "",
-			    wp->fd == -1 ? " (dead)" : "");
-			break;
-		}
+		format_free(ft);
 		n++;
 	}
 }
diff --git a/cmd-list-sessions.c b/cmd-list-sessions.c
index 5791800c..1ddc574d 100644
--- a/cmd-list-sessions.c
+++ b/cmd-list-sessions.c
@@ -31,40 +31,45 @@ int	cmd_list_sessions_exec(struct cmd *, struct cmd_ctx *);
 
 const struct cmd_entry cmd_list_sessions_entry = {
 	"list-sessions", "ls",
-	"", 0, 0,
-	"",
+	"F:", 0, 0,
+	"[-F format]",
 	0,
 	NULL,
 	NULL,
 	cmd_list_sessions_exec
 };
 
-/* ARGSUSED */
 int
-cmd_list_sessions_exec(unused struct cmd *self, struct cmd_ctx *ctx)
+cmd_list_sessions_exec(struct cmd *self, struct cmd_ctx *ctx)
 {
+	struct args		*args = self->args;
 	struct session		*s;
-	struct session_group	*sg;
-	char			*tim, tmp[64];
-	u_int			 idx;
-	time_t			 t;
+	u_int		 	 n;
+	struct format_tree	*ft;
+	const char		*template;
+	char			*line;
 
+	template = args_get(args, 'F');
+	if (template == NULL) {
+		template = "#{session_name}: #{session_windows} windows "
+		    "(created #{session_created_string}) [#{session_width}x"
+		    "#{session_height}]#{?session_grouped, (group ,}"
+		    "#{session_group}#{?session_grouped,),}"
+		    "#{?session_attached, (attached),}";
+	}
+
+	n = 0;
 	RB_FOREACH(s, sessions, &sessions) {
-		sg = session_group_find(s);
-		if (sg == NULL)
-			*tmp = '\0';
-		else {
-			idx = session_group_index(sg);
-			xsnprintf(tmp, sizeof tmp, " (group %u)", idx);
-		}
+		ft = format_create();
+		format_add(ft, "line", "%u", n);
+		format_session(ft, s);
 
-		t = s->creation_time.tv_sec;
-		tim = ctime(&t);
-		*strchr(tim, '\n') = '\0';
+		line = format_expand(ft, template);
+		ctx->print(ctx, "%s", line);
+		xfree(line);
 
-		ctx->print(ctx, "%s: %u windows (created %s) [%ux%u]%s%s",
-		    s->name, winlink_count(&s->windows), tim, s->sx, s->sy,
-		    tmp, s->flags & SESSION_UNATTACHED ? "" : " (attached)");
+		format_free(ft);
+		n++;
 	}
 
 	return (0);
diff --git a/cmd-list-windows.c b/cmd-list-windows.c
index 0bfe94ed..1b34b1c2 100644
--- a/cmd-list-windows.c
+++ b/cmd-list-windows.c
@@ -28,13 +28,14 @@
 
 int	cmd_list_windows_exec(struct cmd *, struct cmd_ctx *);
 
-void	cmd_list_windows_server(struct cmd_ctx *);
-void	cmd_list_windows_session(struct session *, struct cmd_ctx *, int);
+void	cmd_list_windows_server(struct cmd *, struct cmd_ctx *);
+void	cmd_list_windows_session(
+	    struct cmd *, struct session *, struct cmd_ctx *, int);
 
 const struct cmd_entry cmd_list_windows_entry = {
 	"list-windows", "lsw",
-	"at:", 0, 0,
-	"[-a] " CMD_TARGET_SESSION_USAGE,
+	"aF:t:", 0, 0,
+	"[-a] [-F format] " CMD_TARGET_SESSION_USAGE,
 	0,
 	NULL,
 	NULL,
@@ -48,45 +49,69 @@ cmd_list_windows_exec(struct cmd *self, struct cmd_ctx *ctx)
 	struct session	*s;
 
 	if (args_has(args, 'a'))
-		cmd_list_windows_server(ctx);
+		cmd_list_windows_server(self, ctx);
 	else {
 		s = cmd_find_session(ctx, args_get(args, 't'), 0);
 		if (s == NULL)
 			return (-1);
-		cmd_list_windows_session(s, ctx, 0);
+		cmd_list_windows_session(self, s, ctx, 0);
 	}
 
 	return (0);
 }
 
 void
-cmd_list_windows_server(struct cmd_ctx *ctx)
+cmd_list_windows_server(struct cmd *self, struct cmd_ctx *ctx)
 {
 	struct session	*s;
 
 	RB_FOREACH(s, sessions, &sessions)
-		cmd_list_windows_session(s, ctx, 1);
+		cmd_list_windows_session(self, s, ctx, 1);
 }
 
 void
-cmd_list_windows_session(struct session *s, struct cmd_ctx *ctx, int type)
+cmd_list_windows_session(
+    struct cmd *self, struct session *s, struct cmd_ctx *ctx, int type)
 {
-	struct winlink	*wl;
-	char		*layout;
+	struct args		*args = self->args;
+	struct winlink		*wl;
+	u_int			n;
+	struct format_tree	*ft;
+	const char		*template;
+	char			*line;
 
-	RB_FOREACH(wl, winlinks, &s->windows) {
-		layout = layout_dump(wl->window);
-		if (type) {
-			ctx->print(ctx, "%s:%d: %s [%ux%u] [layout %s]%s",
-			    s->name, wl->idx, wl->window->name, wl->window->sx,
-			    wl->window->sy, layout,
-			    wl == s->curw ? " (active)" : "");
-		} else {
-			ctx->print(ctx, "%d: %s [%ux%u] [layout %s]%s",
-			    wl->idx, wl->window->name, wl->window->sx,
-			    wl->window->sy, layout,
-			    wl == s->curw ? " (active)" : "");
+	template = args_get(args, 'F');
+	if (template == NULL) {
+		switch (type) {
+		case 0:
+			template = "#{window_index}: "
+			    "#{window_name} "
+			    "[#{window_width}x#{window_height}] "
+			    "[layout #{window_layout}]"
+			    "#{?window_active, (active),}";
+			break;
+		case 1:
+			template = "#{session_name):#{window_index}: "
+			    "#{window_name} "
+			    "[#{window_width}x#{window_height}] "
+			    "[layout #{window_layout}]"
+			    "#{?window_active, (active),}";
+			break;
 		}
-		xfree(layout);
+	}
+
+	n = 0;
+	RB_FOREACH(wl, winlinks, &s->windows) {
+		ft = format_create();
+		format_add(ft, "line", "%u", n);
+		format_session(ft, s);
+		format_winlink(ft, s, wl);
+
+		line = format_expand(ft, template);
+		ctx->print(ctx, "%s", line);
+		xfree(line);
+
+		format_free(ft);
+		n++;
 	}
 }
diff --git a/format.c b/format.c
new file mode 100644
index 00000000..2924c8c0
--- /dev/null
+++ b/format.c
@@ -0,0 +1,346 @@
+/* $Id$ */
+
+/*
+ * Copyright (c) 2011 Nicholas Marriott <nicm@users.sourceforge.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+
+#include <netdb.h>
+#include <stdarg.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "tmux.h"
+
+/*
+ * Build a list of key-value pairs and use them to expand #{key} entries in a
+ * string.
+ */
+
+int	format_replace(struct format_tree *,
+	    const char *, size_t, char **, size_t *, size_t *);
+
+/* Format key-value replacement entry. */
+RB_GENERATE(format_tree, format_entry, entry, format_cmp);
+
+/* Format tree comparison function. */
+int
+format_cmp(struct format_entry *fe1, struct format_entry *fe2)
+{
+	return (strcmp(fe1->key, fe2->key));
+}
+
+/* Single-character aliases. */
+const char *format_aliases[26] = {
+	NULL,		/* A */
+	NULL,		/* B */
+	NULL,		/* C */
+	"pane_id",	/* D */
+	NULL,		/* E */
+	"window_flags",	/* F */
+	NULL,		/* G */
+	"host",		/* H */
+	"window_index",	/* I */
+	NULL,		/* J */
+	NULL,		/* K */
+	NULL,		/* L */
+	NULL,		/* M */
+	NULL,		/* N */
+	NULL,		/* O */
+	"pane_index",	/* P */
+	NULL,		/* Q */
+	NULL,		/* R */
+	"session_name",	/* S */
+	"pane_title",	/* T */
+	NULL,		/* U */
+	NULL,		/* V */
+	"window_name",	/* W */
+	NULL,		/* X */
+	NULL,		/* Y */
+	NULL 		/* Z */
+};
+
+/* Create a new tree. */
+struct format_tree *
+format_create(void)
+{
+	struct format_tree	*ft;
+	char			 host[MAXHOSTNAMELEN];
+
+	ft = xmalloc(sizeof *ft);
+	RB_INIT(ft);
+
+	if (gethostname(host, sizeof host) == 0)
+		format_add(ft, "host", "%s", host);
+
+	return (ft);
+}
+
+/* Free a tree. */
+void
+format_free(struct format_tree *ft)
+{
+	struct format_entry	*fe, *fe_next;
+
+	fe_next = RB_MIN(format_tree, ft);
+	while (fe_next != NULL) {
+		fe = fe_next;
+		fe_next = RB_NEXT(format_tree, ft, fe);
+
+		RB_REMOVE(format_tree, ft, fe);
+		xfree(fe->value);
+		xfree(fe->key);
+		xfree(fe);
+	}
+
+	xfree (ft);
+}
+
+/* Add a key-value pair. */
+void
+format_add(struct format_tree *ft, const char *key, const char *fmt, ...)
+{
+	struct format_entry	*fe;
+	va_list			 ap;
+
+	fe = xmalloc(sizeof *fe);
+	fe->key = xstrdup(key);
+
+	va_start(ap, fmt);
+	xvasprintf(&fe->value, fmt, ap);
+	va_end(ap);
+
+	RB_INSERT(format_tree, ft, fe);
+}
+
+/* Find a format entry. */
+const char *
+format_find(struct format_tree *ft, const char *key)
+{
+	struct format_entry	*fe, fe_find;
+
+	fe_find.key = (char *) key;
+	fe = RB_FIND(format_tree, ft, &fe_find);
+	if (fe == NULL)
+		return (NULL);
+	return (fe->value);
+}
+
+/*
+ * Replace a key/value pair in buffer. #{blah} is expanded directly,
+ * #{?blah,a,b} is replace with a if blah exists and is nonzero else b.
+ */
+int
+format_replace(struct format_tree *ft,
+    const char *key, size_t keylen, char **buf, size_t *len, size_t *off)
+{
+	char		*copy, *ptr;
+	const char	*value;
+	size_t		 valuelen;
+
+	/* Make a copy of the key. */
+	copy = xmalloc(keylen + 1);
+	memcpy(copy, key, keylen);
+	copy[keylen] = '\0';
+
+	/*
+	 * Is this a conditional? If so, check it exists and extract either the
+	 * first or second element. If not, look up the key directly.
+	 */
+	if (*copy == '?') {
+		ptr = strchr(copy, ',');
+		if (ptr == NULL)
+			goto fail;
+		*ptr = '\0';
+
+		value = format_find(ft, copy + 1);
+		if (value != NULL && (value[0] != '0' || value[1] != '\0')) {
+			value = ptr + 1;
+			ptr = strchr(value, ',');
+			if (ptr == NULL)
+				goto fail;
+			*ptr = '\0';
+		} else {
+			ptr = strchr(ptr + 1, ',');
+			if (ptr == NULL)
+				goto fail;
+			value = ptr + 1;
+		}
+	} else {
+		value = format_find(ft, copy);
+		if (value == NULL)
+			value = "";
+	}
+	valuelen = strlen(value);
+
+	/* Expand the buffer and copy in the value. */
+	while (*len - *off < valuelen + 1) {
+		*buf = xrealloc(*buf, 2, *len);
+		*len *= 2;
+	}
+	memcpy(*buf + *off, value, valuelen);
+	*off += valuelen;
+
+	xfree(copy);
+	return (0);
+
+fail:
+	xfree(copy);
+	return (-1);
+}
+
+/* Expand keys in a template. */
+char *
+format_expand(struct format_tree *ft, const char *fmt)
+{
+	char		*buf, *ptr;
+	const char	*s;
+	size_t		 off, len, n;
+	int     	 ch;
+
+	len = 64;
+	buf = xmalloc(len);
+	off = 0;
+
+	while (*fmt != '\0') {
+		if (*fmt != '#') {
+			while (len - off < 2) {
+				buf = xrealloc(buf, 2, len);
+				len *= 2;
+			}
+			buf[off++] = *fmt++;
+			continue;
+		}
+		fmt++;
+
+		ch = (u_char) *fmt++;
+		switch (ch) {
+		case '{':
+			ptr = strchr(fmt, '}');
+			if (ptr == NULL)
+				break;
+			n = ptr - fmt;
+
+			if (format_replace(ft, fmt, n, &buf, &len, &off) != 0)
+				break;
+			fmt += n + 1;
+			continue;
+		default:
+			if (ch >= 'A' && ch <= 'Z') {
+				s = format_aliases[ch - 'A'];
+				if (s != NULL) {
+					n = strlen(s);
+					if (format_replace (
+					    ft, s, n, &buf, &len, &off) != 0)
+						break;
+					continue;
+				}
+			}
+			while (len - off < 2) {
+				buf = xrealloc(buf, 2, len);
+				len *= 2;
+			}
+			buf[off++] = ch;
+			continue;
+		}
+
+		break;
+	}
+	buf[off] = '\0';
+
+	return (buf);
+}
+
+/* Set default format keys for a session. */
+void
+format_session(struct format_tree *ft, struct session *s)
+{
+	struct session_group	*sg;
+	char			*tim;
+	time_t			 t;
+
+	format_add(ft, "session_name", "%s", s->name);
+	format_add(ft, "session_windows", "%u", winlink_count(&s->windows));
+	format_add(ft, "session_width", "%u", s->sx);
+	format_add(ft, "session_height", "%u", s->sy);
+
+	sg = session_group_find(s);
+	format_add(ft, "session_grouped", "%d", sg != NULL);
+	if (sg != NULL)
+		format_add(ft, "session_group", "%u", session_group_index(sg));
+
+	t = s->creation_time.tv_sec;
+	format_add(ft, "session_created", "%ld", (long) t);
+	tim = ctime(&t);
+	*strchr(tim, '\n') = '\0';
+	format_add(ft, "session_created_string", "%s", tim);
+
+	if (s->flags & SESSION_UNATTACHED)
+		format_add(ft, "session_attached", "%d", 0);
+	else
+		format_add(ft, "session_attached", "%d", 1);
+}
+
+/* Set default format keys for a winlink. */
+void
+format_winlink(struct format_tree *ft, struct session *s, struct winlink *wl)
+{
+	struct window	*w = wl->window;
+	char		*layout, *flags;
+
+	layout = layout_dump(w);
+	flags = window_printable_flags(s, wl);
+
+	format_add(ft, "window_index", "%d", wl->idx);
+	format_add(ft, "window_name", "%s", w->name);
+	format_add(ft, "window_width", "%u", w->sx);
+	format_add(ft, "window_height", "%u", w->sy);
+	format_add(ft, "window_flags", "%s", flags);
+	format_add(ft, "window_layout", "%s", layout);
+	format_add(ft, "window_active", "%d", wl == s->curw);
+
+	xfree(flags);
+	xfree(layout);
+}
+
+/* Set default format keys for a window pane. */
+void
+format_window_pane(struct format_tree *ft, struct window_pane *wp)
+{
+	struct grid		*gd = wp->base.grid;
+	struct grid_line	*gl;
+	unsigned long long	 size;
+	u_int			 i;
+
+	size = 0;
+	for (i = 0; i < gd->hsize; i++) {
+		gl = &gd->linedata[i];
+		size += gl->cellsize * sizeof *gl->celldata;
+		size += gl->utf8size * sizeof *gl->utf8data;
+	}
+	size += gd->hsize * sizeof *gd->linedata;
+
+	format_add(ft, "pane_width", "%u", wp->sx);
+	format_add(ft, "pane_height", "%u", wp->sy);
+	format_add(ft, "pane_title", "%s", wp->base.title);
+	format_add(ft, "history_size", "%u", gd->hsize);
+	format_add(ft, "history_limit", "%u", gd->hlimit);
+	format_add(ft, "history_bytes", "%llu", size);
+	format_add(ft, "pane_id", "%%%u", wp->id);
+	format_add(ft, "pane_active", "%d", wp == wp->window->active);
+	format_add(ft, "pane_dead", "%d", wp->fd == -1);
+}
diff --git a/tmux.1 b/tmux.1
index 1607621f..9ba3bc24 100644
--- a/tmux.1
+++ b/tmux.1
@@ -14,7 +14,7 @@
 .\" IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 .\" OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: August 24 2011 $
+.Dd $Mdocdate: August 26 2011 $
 .Dt TMUX 1
 .Os
 .Sh NAME
@@ -621,6 +621,7 @@ is specified, list only clients connected to that session.
 List the syntax of all commands supported by
 .Nm .
 .It Ic list-sessions
+.Op Fl F Ar format
 .D1 (alias: Ic ls )
 List all sessions managed by the server.
 .It Ic lock-client Op Fl t Ar target-client
@@ -630,6 +631,11 @@ Lock
 see the
 .Ic lock-server
 command.
+For the meaning of the
+.Fl F
+flag, see the
+.Sx FORMATS
+section.
 .It Ic lock-session Op Fl t Ar target-session
 .D1 (alias: Ic locks )
 Lock all clients attached to
@@ -1151,6 +1157,7 @@ If
 is given, the newly linked window is not selected.
 .It Xo Ic list-panes
 .Op Fl as
+.Op Fl F Ar format
 .Op Fl t Ar target
 .Xc
 .D1 (alias: Ic lsp )
@@ -1169,6 +1176,7 @@ If neither is given,
 is a window (or the current window).
 .It Xo Ic list-windows
 .Op Fl a
+.Op Fl F Ar format
 .Op Fl t Ar target-session
 .Xc
 .D1 (alias: Ic lsw )
@@ -1177,6 +1185,11 @@ If
 is given, list all windows on the server.
 Otherwise, list windows in the current session or in
 .Ar target-session .
+For the meaning of the
+.Fl F
+flag, see the
+.Sx FORMATS
+section.
 .It Xo Ic move-window
 .Op Fl dk
 .Op Fl s Ar src-window
@@ -2539,6 +2552,70 @@ or the global window options if
 .Fl g
 is used.
 .El
+.Sh FORMATS
+The
+.Ic list-sessions ,
+.Ic list-windows
+and
+.Ic list-panes
+commands accept the
+.Fl F
+flag with a
+.Ar format
+argument.
+This is a string which controls the output format of the command.
+Special character sequences are replaced as documented under the
+.Ic status-left
+option and an additional long form is accepted.
+Replacement variables are enclosed in
+.Ql #{
+and
+.Ql } ,
+for example
+.Ql #{session_name}
+is equivalent to
+.Ql #S .
+Conditionals are also accepted by prefixing with
+.Ql ?
+and separating two alternatives with a comma;
+if the specified variable exists and is not zero, the first alternative
+is chosen, otherwise the second is used. For example
+.Ql #{?session_attached,attached,not attached}
+will include the string
+.Ql attached
+if the session is attached and the string
+.Ql not attached
+if it is unattached.
+.Pp
+The following variables are available, where appropriate:
+.Bl -column "session_created_string" "Replaced with" -offset indent
+.It Sy "Variable name" Ta Sy "Replaced with"
+.It Li "host" Ta "Hostname of local host"
+.It Li "line" Ta "Line number in the list"
+.It Li "pane_active" Ta "1 if active pane"
+.It Li "pane_dead" Ta "1 if pane is dead"
+.It Li "pane_height" Ta "Height of pane"
+.It Li "pane_id" Ta "Unique pane id"
+.It Li "pane_title" Ta "Title of pane"
+.It Li "pane_width" Ta "Width of pane"
+.It Li "session_attached" Ta "1 if session attached"
+.It Li "session_created" Ta "Integer time session created"
+.It Li "session_created_string" Ta "String time session created"
+.It Li "session_group" Ta "Number of session group"
+.It Li "session_grouped" Ta "1 if session in a group"
+.It Li "session_height" Ta "Height of session"
+.It Li "session_name" Ta "Name of session"
+.It Li "session_width" Ta "Width of session"
+.It Li "session_windows" Ta "Number of windows in session"
+.It Li "window_active" Ta "1 if window active"
+.It Li "window_flags" Ta "Window flags"
+.It Li "window_height" Ta "Height of window"
+.It Li "window_index" Ta "Index of window"
+.It Li "window_layout" Ta "Window layout description"
+.It Li "window_name" Ta "Name of window"
+.It Li "window_width" Ta "Width of window"
+.El
+.Pp
 .Sh ENVIRONMENT
 When the server is started,
 .Nm
diff --git a/tmux.h b/tmux.h
index 4458813b..74add288 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1299,6 +1299,15 @@ struct options_table_entry {
 	long long		default_num;
 };
 
+/* Tree of format entries. */
+struct format_entry {
+	char		       *key;
+	char		       *value;
+
+	RB_ENTRY(format_entry)	entry;
+};
+RB_HEAD(format_tree, format_entry);
+
 /* List of configuration causes. */
 ARRAY_DECL(causelist, char *);
 
@@ -1341,6 +1350,20 @@ extern struct causelist cfg_causes;
 void printflike2 cfg_add_cause(struct causelist *, const char *, ...);
 int		 load_cfg(const char *, struct cmd_ctx *, struct causelist *);
 
+/* format.c */
+int		 format_cmp(struct format_entry *, struct format_entry *);
+RB_PROTOTYPE(format_tree, format_entry, entry, format_cmp);
+struct format_tree *format_create(void);
+void		 format_free(struct format_tree *);
+void		 format_add(
+		     struct format_tree *, const char *, const char *, ...);
+const char	*format_find(struct format_tree *, const char *);
+char		*format_expand(struct format_tree *, const char *);
+void		 format_session(struct format_tree *, struct session *);
+void		 format_winlink(
+		     struct format_tree *, struct session *, struct winlink *);
+void		 format_window_pane(struct format_tree *, struct window_pane *);
+
 /* mode-key.c */
 extern const struct mode_key_table mode_key_tables[];
 extern struct mode_key_tree mode_key_tree_vi_edit;