diff --git a/Makefile b/Makefile
index 40bdcff696..60496ff957 100644
--- a/Makefile
+++ b/Makefile
@@ -262,7 +262,8 @@ LIB_OBJS = \
 	revision.o pager.o tree-walk.o xdiff-interface.o \
 	write_or_die.o trace.o list-objects.o grep.o \
 	alloc.o merge-file.o path-list.o help.o unpack-trees.o $(DIFF_OBJS) \
-	color.o wt-status.o archive-zip.o archive-tar.o shallow.o utf8.o
+	color.o wt-status.o archive-zip.o archive-tar.o shallow.o utf8.o \
+	convert.o
 
 BUILTIN_OBJS = \
 	builtin-add.o \
diff --git a/cache.h b/cache.h
index c62b0b090d..9c019e8bba 100644
--- a/cache.h
+++ b/cache.h
@@ -201,6 +201,7 @@ extern const char *apply_default_whitespace;
 extern int zlib_compression_level;
 extern size_t packed_git_window_size;
 extern size_t packed_git_limit;
+extern int auto_crlf;
 
 #define GIT_REPO_VERSION 0
 extern int repository_format_version;
@@ -468,4 +469,8 @@ extern int nfvasprintf(char **str, const char *fmt, va_list va);
 extern void trace_printf(const char *format, ...);
 extern void trace_argv_printf(const char **argv, int count, const char *format, ...);
 
+/* convert.c */
+extern int convert_to_git(const char *path, char **bufp, unsigned long *sizep);
+extern int convert_to_working_tree(const char *path, char **bufp, unsigned long *sizep);
+
 #endif /* CACHE_H */
diff --git a/config.c b/config.c
index d82107124a..ffe02129a5 100644
--- a/config.c
+++ b/config.c
@@ -324,6 +324,11 @@ int git_default_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.autocrlf")) {
+		auto_crlf = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "user.name")) {
 		strlcpy(git_default_name, value, sizeof(git_default_name));
 		return 0;
diff --git a/convert.c b/convert.c
new file mode 100644
index 0000000000..13beb70582
--- /dev/null
+++ b/convert.c
@@ -0,0 +1,186 @@
+#include "cache.h"
+/*
+ * convert.c - convert a file when checking it out and checking it in.
+ *
+ * This should use the pathname to decide on whether it wants to do some
+ * more interesting conversions (automatic gzip/unzip, general format
+ * conversions etc etc), but by default it just does automatic CRLF<->LF
+ * translation when the "auto_crlf" option is set.
+ */
+
+struct text_stat {
+	/* CR, LF and CRLF counts */
+	unsigned cr, lf, crlf;
+
+	/* These are just approximations! */
+	unsigned printable, nonprintable;
+};
+
+static void gather_stats(const char *buf, unsigned long size, struct text_stat *stats)
+{
+	unsigned long i;
+
+	memset(stats, 0, sizeof(*stats));
+
+	for (i = 0; i < size; i++) {
+		unsigned char c = buf[i];
+		if (c == '\r') {
+			stats->cr++;
+			if (i+1 < size && buf[i+1] == '\n')
+				stats->crlf++;
+			continue;
+		}
+		if (c == '\n') {
+			stats->lf++;
+			continue;
+		}
+		if (c == 127)
+			/* DEL */
+			stats->nonprintable++;
+		else if (c < 32) {
+			switch (c) {
+				/* BS, HT, ESC and FF */
+			case '\b': case '\t': case '\033': case '\014':
+				stats->printable++;
+				break;
+			default:
+				stats->nonprintable++;
+			}
+		}
+		else
+			stats->printable++;
+	}
+}
+
+/*
+ * The same heuristics as diff.c::mmfile_is_binary()
+ */
+static int is_binary(unsigned long size, struct text_stat *stats)
+{
+
+	if ((stats->printable >> 7) < stats->nonprintable)
+		return 1;
+	/*
+	 * Other heuristics? Average line length might be relevant,
+	 * as might LF vs CR vs CRLF counts..
+	 *
+	 * NOTE! It might be normal to have a low ratio of CRLF to LF
+	 * (somebody starts with a LF-only file and edits it with an editor
+	 * that adds CRLF only to lines that are added..). But do  we
+	 * want to support CR-only? Probably not.
+	 */
+	return 0;
+}
+
+int convert_to_git(const char *path, char **bufp, unsigned long *sizep)
+{
+	char *buffer, *nbuf;
+	unsigned long size, nsize;
+	struct text_stat stats;
+
+	/*
+	 * FIXME! Other pluggable conversions should go here,
+	 * based on filename patterns. Right now we just do the
+	 * stupid auto-CRLF one.
+	 */
+	if (!auto_crlf)
+		return 0;
+
+	size = *sizep;
+	if (!size)
+		return 0;
+	buffer = *bufp;
+
+	gather_stats(buffer, size, &stats);
+
+	/* No CR? Nothing to convert, regardless. */
+	if (!stats.cr)
+		return 0;
+
+	/*
+	 * We're currently not going to even try to convert stuff
+	 * that has bare CR characters. Does anybody do that crazy
+	 * stuff?
+	 */
+	if (stats.cr != stats.crlf)
+		return 0;
+
+	/*
+	 * And add some heuristics for binary vs text, of course...
+	 */
+	if (is_binary(size, &stats))
+		return 0;
+
+	/*
+	 * Ok, allocate a new buffer, fill it in, and return true
+	 * to let the caller know that we switched buffers on it.
+	 */
+	nsize = size - stats.crlf;
+	nbuf = xmalloc(nsize);
+	*bufp = nbuf;
+	*sizep = nsize;
+	do {
+		unsigned char c = *buffer++;
+		if (c != '\r')
+			*nbuf++ = c;
+	} while (--size);
+
+	return 1;
+}
+
+int convert_to_working_tree(const char *path, char **bufp, unsigned long *sizep)
+{
+	char *buffer, *nbuf;
+	unsigned long size, nsize;
+	struct text_stat stats;
+	unsigned char last;
+
+	/*
+	 * FIXME! Other pluggable conversions should go here,
+	 * based on filename patterns. Right now we just do the
+	 * stupid auto-CRLF one.
+	 */
+	if (!auto_crlf)
+		return 0;
+
+	size = *sizep;
+	if (!size)
+		return 0;
+	buffer = *bufp;
+
+	gather_stats(buffer, size, &stats);
+
+	/* No LF? Nothing to convert, regardless. */
+	if (!stats.lf)
+		return 0;
+
+	/* Was it already in CRLF format? */
+	if (stats.lf == stats.crlf)
+		return 0;
+
+	/* If we have any bare CR characters, we're not going to touch it */
+	if (stats.cr != stats.crlf)
+		return 0;
+
+	if (is_binary(size, &stats))
+		return 0;
+
+	/*
+	 * Ok, allocate a new buffer, fill it in, and return true
+	 * to let the caller know that we switched buffers on it.
+	 */
+	nsize = size + stats.lf - stats.crlf;
+	nbuf = xmalloc(nsize);
+	*bufp = nbuf;
+	*sizep = nsize;
+	last = 0;
+	do {
+		unsigned char c = *buffer++;
+		if (c == '\n' && last != '\r')
+			*nbuf++ = '\r';
+		*nbuf++ = c;
+		last = c;
+	} while (--size);
+
+	return 1;
+}
diff --git a/diff.c b/diff.c
index 13b9b6c560..561587cace 100644
--- a/diff.c
+++ b/diff.c
@@ -1332,6 +1332,9 @@ int diff_populate_filespec(struct diff_filespec *s, int size_only)
 	    reuse_worktree_file(s->path, s->sha1, 0)) {
 		struct stat st;
 		int fd;
+		char *buf;
+		unsigned long size;
+
 		if (lstat(s->path, &st) < 0) {
 			if (errno == ENOENT) {
 			err_empty:
@@ -1364,7 +1367,19 @@ int diff_populate_filespec(struct diff_filespec *s, int size_only)
 		s->data = xmmap(NULL, s->size, PROT_READ, MAP_PRIVATE, fd, 0);
 		close(fd);
 		s->should_munmap = 1;
-		/* FIXME! CRLF -> LF conversion goes here, based on "s->path" */
+
+		/*
+		 * Convert from working tree format to canonical git format
+		 */
+		buf = s->data;
+		size = s->size;
+		if (convert_to_git(s->path, &buf, &size)) {
+			munmap(s->data, s->size);
+			s->should_munmap = 0;
+			s->data = buf;
+			s->size = size;
+			s->should_free = 1;
+		}
 	}
 	else {
 		char type[20];
diff --git a/entry.c b/entry.c
index c2641ddefd..472a9ef321 100644
--- a/entry.c
+++ b/entry.c
@@ -78,6 +78,9 @@ static int write_entry(struct cache_entry *ce, char *path, struct checkout *stat
 			path, sha1_to_hex(ce->sha1));
 	}
 	switch (ntohl(ce->ce_mode) & S_IFMT) {
+		char *buf;
+		unsigned long nsize;
+
 	case S_IFREG:
 		if (to_tempfile) {
 			strcpy(path, ".merge_file_XXXXXX");
@@ -89,7 +92,18 @@ static int write_entry(struct cache_entry *ce, char *path, struct checkout *stat
 			return error("git-checkout-index: unable to create file %s (%s)",
 				path, strerror(errno));
 		}
-		/* FIXME: LF -> CRLF conversion goes here, based on "ce->name" */
+
+		/*
+		 * Convert from git internal format to working tree format
+		 */
+		buf = new;
+		nsize = size;
+		if (convert_to_working_tree(ce->name, &buf, &nsize)) {
+			free(new);
+			new = buf;
+			size = nsize;
+		}
+
 		wrote = write_in_full(fd, new, size);
 		close(fd);
 		free(new);
diff --git a/environment.c b/environment.c
index 54c22f8248..2fa0960412 100644
--- a/environment.c
+++ b/environment.c
@@ -28,6 +28,7 @@ size_t packed_git_window_size = DEFAULT_PACKED_GIT_WINDOW_SIZE;
 size_t packed_git_limit = DEFAULT_PACKED_GIT_LIMIT;
 int pager_in_use;
 int pager_use_color = 1;
+int auto_crlf = 0;
 
 static const char *git_dir;
 static char *git_object_dir, *git_index_file, *git_refs_dir, *git_graft_file;
diff --git a/sha1_file.c b/sha1_file.c
index 8ad7fad825..6ec67b2923 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -2082,7 +2082,7 @@ int index_fd(unsigned char *sha1, int fd, struct stat *st, int write_object, con
 {
 	unsigned long size = st->st_size;
 	void *buf;
-	int ret;
+	int ret, re_allocated = 0;
 
 	buf = "";
 	if (size)
@@ -2091,11 +2091,30 @@ int index_fd(unsigned char *sha1, int fd, struct stat *st, int write_object, con
 
 	if (!type)
 		type = blob_type;
-	/* FIXME: CRLF -> LF conversion here for blobs! We'll need the path! */
+
+	/*
+	 * Convert blobs to git internal format
+	 */
+	if (!strcmp(type, blob_type)) {
+		unsigned long nsize = size;
+		char *nbuf = buf;
+		if (convert_to_git(NULL, &nbuf, &nsize)) {
+			if (size)
+				munmap(buf, size);
+			size = nsize;
+			buf = nbuf;
+			re_allocated = 1;
+		}
+	}
+
 	if (write_object)
 		ret = write_sha1_file(buf, size, type, sha1);
 	else
 		ret = hash_sha1_file(buf, size, type, sha1);
+	if (re_allocated) {
+		free(buf);
+		return ret;
+	}
 	if (size)
 		munmap(buf, size);
 	return ret;