diff --git a/Makefile b/Makefile
index 1fb0ec1705..10ee5e709b 100644
--- a/Makefile
+++ b/Makefile
@@ -945,6 +945,7 @@ LIB_OBJS += pack-revindex.o
 LIB_OBJS += pack-write.o
 LIB_OBJS += packfile.o
 LIB_OBJS += pager.o
+LIB_OBJS += parallel-checkout.o
 LIB_OBJS += parse-options-cb.o
 LIB_OBJS += parse-options.o
 LIB_OBJS += patch-delta.o
diff --git a/entry.c b/entry.c
index 9d79a5671f..6676954431 100644
--- a/entry.c
+++ b/entry.c
@@ -7,6 +7,7 @@
 #include "progress.h"
 #include "fsmonitor.h"
 #include "entry.h"
+#include "parallel-checkout.h"
 
 static void create_directories(const char *path, int path_len,
 			       const struct checkout *state)
@@ -426,8 +427,17 @@ static void mark_colliding_entries(const struct checkout *state,
 	for (i = 0; i < state->istate->cache_nr; i++) {
 		struct cache_entry *dup = state->istate->cache[i];
 
-		if (dup == ce)
-			break;
+		if (dup == ce) {
+			/*
+			 * Parallel checkout creates the files in no particular
+			 * order. So the other side of the collision may appear
+			 * after the given cache_entry in the array.
+			 */
+			if (parallel_checkout_status() == PC_RUNNING)
+				continue;
+			else
+				break;
+		}
 
 		if (dup->ce_flags & (CE_MATCHED | CE_VALID | CE_SKIP_WORKTREE))
 			continue;
@@ -536,6 +546,9 @@ int checkout_entry_ca(struct cache_entry *ce, struct conv_attrs *ca,
 		ca = &ca_buf;
 	}
 
+	if (!enqueue_checkout(ce, ca))
+		return 0;
+
 	return write_entry(ce, path.buf, ca, state, 0);
 }
 
diff --git a/parallel-checkout.c b/parallel-checkout.c
new file mode 100644
index 0000000000..981dbe6ff3
--- /dev/null
+++ b/parallel-checkout.c
@@ -0,0 +1,368 @@
+#include "cache.h"
+#include "entry.h"
+#include "parallel-checkout.h"
+#include "streaming.h"
+
+enum pc_item_status {
+	PC_ITEM_PENDING = 0,
+	PC_ITEM_WRITTEN,
+	/*
+	 * The entry could not be written because there was another file
+	 * already present in its path or leading directories. Since
+	 * checkout_entry_ca() removes such files from the working tree before
+	 * enqueueing the entry for parallel checkout, it means that there was
+	 * a path collision among the entries being written.
+	 */
+	PC_ITEM_COLLIDED,
+	PC_ITEM_FAILED,
+};
+
+struct parallel_checkout_item {
+	/* pointer to a istate->cache[] entry. Not owned by us. */
+	struct cache_entry *ce;
+	struct conv_attrs ca;
+	struct stat st;
+	enum pc_item_status status;
+};
+
+struct parallel_checkout {
+	enum pc_status status;
+	struct parallel_checkout_item *items;
+	size_t nr, alloc;
+};
+
+static struct parallel_checkout parallel_checkout = { 0 };
+
+enum pc_status parallel_checkout_status(void)
+{
+	return parallel_checkout.status;
+}
+
+void init_parallel_checkout(void)
+{
+	if (parallel_checkout.status != PC_UNINITIALIZED)
+		BUG("parallel checkout already initialized");
+
+	parallel_checkout.status = PC_ACCEPTING_ENTRIES;
+}
+
+static void finish_parallel_checkout(void)
+{
+	if (parallel_checkout.status == PC_UNINITIALIZED)
+		BUG("cannot finish parallel checkout: not initialized yet");
+
+	free(parallel_checkout.items);
+	memset(&parallel_checkout, 0, sizeof(parallel_checkout));
+}
+
+static int is_eligible_for_parallel_checkout(const struct cache_entry *ce,
+					     const struct conv_attrs *ca)
+{
+	enum conv_attrs_classification c;
+
+	if (!S_ISREG(ce->ce_mode))
+		return 0;
+
+	c = classify_conv_attrs(ca);
+	switch (c) {
+	case CA_CLASS_INCORE:
+		return 1;
+
+	case CA_CLASS_INCORE_FILTER:
+		/*
+		 * It would be safe to allow concurrent instances of
+		 * single-file smudge filters, like rot13, but we should not
+		 * assume that all filters are parallel-process safe. So we
+		 * don't allow this.
+		 */
+		return 0;
+
+	case CA_CLASS_INCORE_PROCESS:
+		/*
+		 * The parallel queue and the delayed queue are not compatible,
+		 * so they must be kept completely separated. And we can't tell
+		 * if a long-running process will delay its response without
+		 * actually asking it to perform the filtering. Therefore, this
+		 * type of filter is not allowed in parallel checkout.
+		 *
+		 * Furthermore, there should only be one instance of the
+		 * long-running process filter as we don't know how it is
+		 * managing its own concurrency. So, spreading the entries that
+		 * requisite such a filter among the parallel workers would
+		 * require a lot more inter-process communication. We would
+		 * probably have to designate a single process to interact with
+		 * the filter and send all the necessary data to it, for each
+		 * entry.
+		 */
+		return 0;
+
+	case CA_CLASS_STREAMABLE:
+		return 1;
+
+	default:
+		BUG("unsupported conv_attrs classification '%d'", c);
+	}
+}
+
+int enqueue_checkout(struct cache_entry *ce, struct conv_attrs *ca)
+{
+	struct parallel_checkout_item *pc_item;
+
+	if (parallel_checkout.status != PC_ACCEPTING_ENTRIES ||
+	    !is_eligible_for_parallel_checkout(ce, ca))
+		return -1;
+
+	ALLOC_GROW(parallel_checkout.items, parallel_checkout.nr + 1,
+		   parallel_checkout.alloc);
+
+	pc_item = &parallel_checkout.items[parallel_checkout.nr++];
+	pc_item->ce = ce;
+	memcpy(&pc_item->ca, ca, sizeof(pc_item->ca));
+	pc_item->status = PC_ITEM_PENDING;
+
+	return 0;
+}
+
+static int handle_results(struct checkout *state)
+{
+	int ret = 0;
+	size_t i;
+	int have_pending = 0;
+
+	/*
+	 * We first update the successfully written entries with the collected
+	 * stat() data, so that they can be found by mark_colliding_entries(),
+	 * in the next loop, when necessary.
+	 */
+	for (i = 0; i < parallel_checkout.nr; ++i) {
+		struct parallel_checkout_item *pc_item = &parallel_checkout.items[i];
+		if (pc_item->status == PC_ITEM_WRITTEN)
+			update_ce_after_write(state, pc_item->ce, &pc_item->st);
+	}
+
+	for (i = 0; i < parallel_checkout.nr; ++i) {
+		struct parallel_checkout_item *pc_item = &parallel_checkout.items[i];
+
+		switch(pc_item->status) {
+		case PC_ITEM_WRITTEN:
+			/* Already handled */
+			break;
+		case PC_ITEM_COLLIDED:
+			/*
+			 * The entry could not be checked out due to a path
+			 * collision with another entry. Since there can only
+			 * be one entry of each colliding group on the disk, we
+			 * could skip trying to check out this one and move on.
+			 * However, this would leave the unwritten entries with
+			 * null stat() fields on the index, which could
+			 * potentially slow down subsequent operations that
+			 * require refreshing it: git would not be able to
+			 * trust st_size and would have to go to the filesystem
+			 * to see if the contents match (see ie_modified()).
+			 *
+			 * Instead, let's pay the overhead only once, now, and
+			 * call checkout_entry_ca() again for this file, to
+			 * have it's stat() data stored in the index. This also
+			 * has the benefit of adding this entry and its
+			 * colliding pair to the collision report message.
+			 * Additionally, this overwriting behavior is consistent
+			 * with what the sequential checkout does, so it doesn't
+			 * add any extra overhead.
+			 */
+			ret |= checkout_entry_ca(pc_item->ce, &pc_item->ca,
+						 state, NULL, NULL);
+			break;
+		case PC_ITEM_PENDING:
+			have_pending = 1;
+			/* fall through */
+		case PC_ITEM_FAILED:
+			ret = -1;
+			break;
+		default:
+			BUG("unknown checkout item status in parallel checkout");
+		}
+	}
+
+	if (have_pending)
+		error(_("parallel checkout finished with pending entries"));
+
+	return ret;
+}
+
+static int reset_fd(int fd, const char *path)
+{
+	if (lseek(fd, 0, SEEK_SET) != 0)
+		return error_errno("failed to rewind descriptor of %s", path);
+	if (ftruncate(fd, 0))
+		return error_errno("failed to truncate file %s", path);
+	return 0;
+}
+
+static int write_pc_item_to_fd(struct parallel_checkout_item *pc_item, int fd,
+			       const char *path)
+{
+	int ret;
+	struct stream_filter *filter;
+	struct strbuf buf = STRBUF_INIT;
+	char *new_blob;
+	unsigned long size;
+	size_t newsize = 0;
+	ssize_t wrote;
+
+	/* Sanity check */
+	assert(is_eligible_for_parallel_checkout(pc_item->ce, &pc_item->ca));
+
+	filter = get_stream_filter_ca(&pc_item->ca, &pc_item->ce->oid);
+	if (filter) {
+		if (stream_blob_to_fd(fd, &pc_item->ce->oid, filter, 1)) {
+			/* On error, reset fd to try writing without streaming */
+			if (reset_fd(fd, path))
+				return -1;
+		} else {
+			return 0;
+		}
+	}
+
+	new_blob = read_blob_entry(pc_item->ce, &size);
+	if (!new_blob)
+		return error("unable to read sha1 file of %s (%s)", path,
+			     oid_to_hex(&pc_item->ce->oid));
+
+	/*
+	 * checkout metadata is used to give context for external process
+	 * filters. Files requiring such filters are not eligible for parallel
+	 * checkout, so pass NULL.
+	 */
+	ret = convert_to_working_tree_ca(&pc_item->ca, pc_item->ce->name,
+					 new_blob, size, &buf, NULL);
+
+	if (ret) {
+		free(new_blob);
+		new_blob = strbuf_detach(&buf, &newsize);
+		size = newsize;
+	}
+
+	wrote = write_in_full(fd, new_blob, size);
+	free(new_blob);
+	if (wrote < 0)
+		return error("unable to write file %s", path);
+
+	return 0;
+}
+
+static int close_and_clear(int *fd)
+{
+	int ret = 0;
+
+	if (*fd >= 0) {
+		ret = close(*fd);
+		*fd = -1;
+	}
+
+	return ret;
+}
+
+static int check_leading_dirs(const char *path, int len, int prefix_len)
+{
+	const char *slash = path + len;
+
+	while (slash > path && *slash != '/')
+		slash--;
+
+	return has_dirs_only_path(path, slash - path, prefix_len);
+}
+
+static void write_pc_item(struct parallel_checkout_item *pc_item,
+			  struct checkout *state)
+{
+	unsigned int mode = (pc_item->ce->ce_mode & 0100) ? 0777 : 0666;
+	int fd = -1, fstat_done = 0;
+	struct strbuf path = STRBUF_INIT;
+
+	strbuf_add(&path, state->base_dir, state->base_dir_len);
+	strbuf_add(&path, pc_item->ce->name, pc_item->ce->ce_namelen);
+
+	/*
+	 * At this point, leading dirs should have already been created. But if
+	 * a symlink being checked out has collided with one of the dirs, due to
+	 * file system folding rules, it's possible that the dirs are no longer
+	 * present. So we have to check again, and report any path collisions.
+	 */
+	if (!check_leading_dirs(path.buf, path.len, state->base_dir_len)) {
+		pc_item->status = PC_ITEM_COLLIDED;
+		goto out;
+	}
+
+	fd = open(path.buf, O_WRONLY | O_CREAT | O_EXCL, mode);
+
+	if (fd < 0) {
+		if (errno == EEXIST || errno == EISDIR) {
+			/*
+			 * Errors which probably represent a path collision.
+			 * Suppress the error message and mark the item to be
+			 * retried later, sequentially. ENOTDIR and ENOENT are
+			 * also interesting, but check_leading_dirs() should
+			 * have already caught these cases.
+			 */
+			pc_item->status = PC_ITEM_COLLIDED;
+		} else {
+			error_errno("failed to open file %s", path.buf);
+			pc_item->status = PC_ITEM_FAILED;
+		}
+		goto out;
+	}
+
+	if (write_pc_item_to_fd(pc_item, fd, path.buf)) {
+		/* Error was already reported. */
+		pc_item->status = PC_ITEM_FAILED;
+		goto out;
+	}
+
+	fstat_done = fstat_checkout_output(fd, state, &pc_item->st);
+
+	if (close_and_clear(&fd)) {
+		error_errno("unable to close file %s", path.buf);
+		pc_item->status = PC_ITEM_FAILED;
+		goto out;
+	}
+
+	if (state->refresh_cache && !fstat_done && lstat(path.buf, &pc_item->st) < 0) {
+		error_errno("unable to stat just-written file %s",  path.buf);
+		pc_item->status = PC_ITEM_FAILED;
+		goto out;
+	}
+
+	pc_item->status = PC_ITEM_WRITTEN;
+
+out:
+	/*
+	 * No need to check close() return. At this point, either fd is already
+	 * closed, or we are on an error path, that has already been reported.
+	 */
+	close_and_clear(&fd);
+	strbuf_release(&path);
+}
+
+static void write_items_sequentially(struct checkout *state)
+{
+	size_t i;
+
+	for (i = 0; i < parallel_checkout.nr; ++i)
+		write_pc_item(&parallel_checkout.items[i], state);
+}
+
+int run_parallel_checkout(struct checkout *state)
+{
+	int ret;
+
+	if (parallel_checkout.status != PC_ACCEPTING_ENTRIES)
+		BUG("cannot run parallel checkout: uninitialized or already running");
+
+	parallel_checkout.status = PC_RUNNING;
+
+	write_items_sequentially(state);
+	ret = handle_results(state);
+
+	finish_parallel_checkout();
+	return ret;
+}
diff --git a/parallel-checkout.h b/parallel-checkout.h
new file mode 100644
index 0000000000..e6d6fc01ea
--- /dev/null
+++ b/parallel-checkout.h
@@ -0,0 +1,27 @@
+#ifndef PARALLEL_CHECKOUT_H
+#define PARALLEL_CHECKOUT_H
+
+struct cache_entry;
+struct checkout;
+struct conv_attrs;
+
+enum pc_status {
+	PC_UNINITIALIZED = 0,
+	PC_ACCEPTING_ENTRIES,
+	PC_RUNNING,
+};
+
+enum pc_status parallel_checkout_status(void);
+void init_parallel_checkout(void);
+
+/*
+ * Return -1 if parallel checkout is currently not enabled or if the entry is
+ * not eligible for parallel checkout. Otherwise, enqueue the entry for later
+ * write and return 0.
+ */
+int enqueue_checkout(struct cache_entry *ce, struct conv_attrs *ca);
+
+/* Write all the queued entries, returning 0 on success.*/
+int run_parallel_checkout(struct checkout *state);
+
+#endif /* PARALLEL_CHECKOUT_H */
diff --git a/unpack-trees.c b/unpack-trees.c
index a511fadd89..1b1da7485a 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -17,6 +17,7 @@
 #include "object-store.h"
 #include "promisor-remote.h"
 #include "entry.h"
+#include "parallel-checkout.h"
 
 /*
  * Error messages expected by scripts out of plumbing commands such as
@@ -438,7 +439,6 @@ static int check_updates(struct unpack_trees_options *o,
 	if (should_update_submodules())
 		load_gitmodules_file(index, &state);
 
-	enable_delayed_checkout(&state);
 	if (has_promisor_remote()) {
 		/*
 		 * Prefetch the objects that are to be checked out in the loop
@@ -461,6 +461,9 @@ static int check_updates(struct unpack_trees_options *o,
 					   to_fetch.oid, to_fetch.nr);
 		oid_array_clear(&to_fetch);
 	}
+
+	enable_delayed_checkout(&state);
+	init_parallel_checkout();
 	for (i = 0; i < index->cache_nr; i++) {
 		struct cache_entry *ce = index->cache[i];
 
@@ -474,6 +477,7 @@ static int check_updates(struct unpack_trees_options *o,
 		}
 	}
 	stop_progress(&progress);
+	errs |= run_parallel_checkout(&state);
 	errs |= finish_delayed_checkout(&state, NULL);
 	git_attr_set_direction(GIT_ATTR_CHECKIN);
 
