diff --git a/Documentation/git.txt b/Documentation/git.txt
index d00cc3ea5219f73aac79709e683e135548555fd3..ce3058182fead833c45daf02a2806f151b15f61f 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -615,6 +615,13 @@ git Diffs
 	gitlink:git-diff-files[1];
 	gitlink:git-diff-tree[1]
 
+other
+~~~~~
+'GIT_TRACE'::
+	If this variable is set git will print `trace:` messages on
+	stderr telling about alias expansion, built-in command
+	execution and external command execution.
+
 Discussion[[Discussion]]
 ------------------------
 include::README[]
diff --git a/exec_cmd.c b/exec_cmd.c
index c1539d12ce9e350811b5b110206f5577a151e8ef..62f51fcd6e367d2dc7e3dc8d967ee05fd1648d04 100644
--- a/exec_cmd.c
+++ b/exec_cmd.c
@@ -1,5 +1,6 @@
 #include "cache.h"
 #include "exec_cmd.h"
+#include "quote.h"
 #define MAX_ARGS	32
 
 extern char **environ;
@@ -96,9 +97,27 @@ int execv_git_cmd(const char **argv)
 		tmp = argv[0];
 		argv[0] = git_command;
 
+		if (getenv("GIT_TRACE")) {
+			const char **p = argv;
+			fputs("trace: exec:", stderr);
+			while (*p) {
+				fputc(' ', stderr);
+				sq_quote_print(stderr, *p);
+				++p;
+			}
+			putc('\n', stderr);
+			fflush(stderr);
+		}
+
 		/* execve() can only ever return if it fails */
 		execve(git_command, (char **)argv, environ);
 
+		if (getenv("GIT_TRACE")) {
+			fprintf(stderr, "trace: exec failed: %s\n",
+				strerror(errno));
+			fflush(stderr);
+		}
+
 		argv[0] = tmp;
 	}
 	return -1;
diff --git a/git.c b/git.c
index fee71383c6e6ca0374e8356c8b55570d00f93ea9..102735af6c0cfb496a04593ba466a9fbb18f693d 100644
--- a/git.c
+++ b/git.c
@@ -11,6 +11,7 @@
 #include "git-compat-util.h"
 #include "exec_cmd.h"
 #include "cache.h"
+#include "quote.h"
 
 #include "builtin.h"
 
@@ -120,6 +121,18 @@ static int handle_alias(int *argcp, const char ***argv)
 			if (!strcmp(alias_command, new_argv[0]))
 				die("recursive alias: %s", alias_command);
 
+			if (getenv("GIT_TRACE")) {
+				int i;
+				fprintf(stderr, "trace: alias expansion: %s =>",
+					alias_command);
+				for (i = 0; i < count; ++i) {
+					fputc(' ', stderr);
+					sq_quote_print(stderr, new_argv[i]);
+				}
+				fputc('\n', stderr);
+				fflush(stderr);
+			}
+
 			/* insert after command name */
 			if (*argcp > 1) {
 				new_argv = realloc(new_argv, sizeof(char*) *
@@ -203,6 +216,18 @@ static void handle_internal_command(int argc, const char **argv, char **envp)
 		struct cmd_struct *p = commands+i;
 		if (strcmp(p->cmd, cmd))
 			continue;
+
+		if (getenv("GIT_TRACE")) {
+			int i;
+			fprintf(stderr, "trace: built-in: git");
+			for (i = 0; i < argc; ++i) {
+				fputc(' ', stderr);
+				sq_quote_print(stderr, argv[i]);
+			}
+			putc('\n', stderr);
+			fflush(stderr);
+		}
+
 		exit(p->fn(argc, argv, envp));
 	}
 }
diff --git a/quote.c b/quote.c
index 1910d000a5d288734aaea24da617481223ff9f56..e220dcc280d9ed6be2e2357e2660c7e828f3631b 100644
--- a/quote.c
+++ b/quote.c
@@ -45,6 +45,23 @@ size_t sq_quote_buf(char *dst, size_t n, const char *src)
 	return len;
 }
 
+void sq_quote_print(FILE *stream, const char *src)
+{
+	char c;
+
+	fputc('\'', stream);
+	while ((c = *src++)) {
+		if (need_bs_quote(c)) {
+			fputs("'\\", stream);
+			fputc(c, stream);
+			fputc('\'', stream);
+		} else {
+			fputc(c, stream);
+		}
+	}
+	fputc('\'', stream);
+}
+
 char *sq_quote(const char *src)
 {
 	char *buf;
diff --git a/quote.h b/quote.h
index c1ab3788e6d69318638142ebeffc690318a0489a..fc5481e78a6baad9ad72014318a9d0bfdd495b6b 100644
--- a/quote.h
+++ b/quote.h
@@ -29,6 +29,7 @@
  */
 
 extern char *sq_quote(const char *src);
+extern void sq_quote_print(FILE *stream, const char *src);
 extern size_t sq_quote_buf(char *dst, size_t n, const char *src);
 
 /* This unwraps what sq_quote() produces in place, but returns
diff --git a/t/test-lib.sh b/t/test-lib.sh
index b0d7990a669cb053e5112bd459e9ecaffbd4c504..470a909891bc1358163af91513972ce7d0c702c0 100755
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -28,6 +28,7 @@ unset GIT_DIR
 unset GIT_EXTERNAL_DIFF
 unset GIT_INDEX_FILE
 unset GIT_OBJECT_DIRECTORY
+unset GIT_TRACE
 unset SHA1_FILE_DIRECTORIES
 unset SHA1_FILE_DIRECTORY
 export GIT_AUTHOR_EMAIL GIT_AUTHOR_NAME