diff --git a/main/Makemodule.am b/main/Makemodule.am
index d8af480..be62c48 100644
--- a/main/Makemodule.am
+++ b/main/Makemodule.am
@@ -22,6 +22,10 @@ pkg_SOURCES += main/cmd/install/collect.c main/cmd/install/install.c
 pkg_SOURCES += main/cmd/install/install.h main/cmd/install/pkglist.c
 pkg_SOURCES += main/cmd/install/tsort.c
 
+# buildstrategy command
+pkg_SOURCES += main/cmd/buildstrategy/buildstrategy.h
+pkg_SOURCES += main/cmd/buildstrategy/buildstrategy.c
+
 # unpack command
 pkg_SOURCES += main/cmd/unpack.c
 
diff --git a/main/cmd/buildstrategy/buildstrategy.c b/main/cmd/buildstrategy/buildstrategy.c
new file mode 100644
index 0000000..57e0a4f
--- /dev/null
+++ b/main/cmd/buildstrategy/buildstrategy.c
@@ -0,0 +1,336 @@
+#include "buildstrategy.h"
+
+typedef int (*line_handler_t)(const char *lhs, const char *rhs);
+
+static int foreach_line(const char *filename, line_handler_t cb)
+{
+	FILE *f = fopen(filename, "r");
+
+	for (;;) {
+		char *line = NULL, *rhs, *lhs, *ptr;
+		size_t n = 0;
+		ssize_t ret;
+
+		errno = 0;
+		ret = getline(&line, &n, f);
+
+		if (ret < 0) {
+			if (errno == 0) {
+				free(line);
+				break;
+			}
+			perror(filename);
+			free(line);
+			fclose(f);
+			return -1;
+		}
+
+		rhs = strchr(line, ',');
+		if (rhs == NULL) {
+			free(line);
+			continue;
+		}
+
+		*(rhs++) = '\0';
+		while (isspace(*rhs))
+			++rhs;
+
+		ptr = rhs;
+		while (*ptr != '\0' && !isspace(*ptr))
+			++ptr;
+		*ptr = '\0';
+
+		lhs = line;
+		while (isspace(*lhs))
+			++lhs;
+
+		if (*lhs == '\0' || *rhs == '\0') {
+			free(line);
+			continue;
+		}
+
+		if (cb(lhs, rhs)) {
+			free(line);
+			fclose(f);
+			return -1;
+		}
+
+		free(line);
+	}
+
+	fclose(f);
+	return 0;
+}
+
+/*****************************************************************************/
+
+static hash_table_t tbl_provides;
+static hash_table_t tbl_sourcepkgs;
+
+static int handle_depends(const char *sourcepkg, const char *binpkg)
+{
+	source_pkg_t *src, *dep;
+	size_t count;
+	void *new;
+
+	src = hash_table_lookup(&tbl_sourcepkgs, sourcepkg);
+	if (src == NULL)
+		return 0;
+
+	dep = hash_table_lookup(&tbl_provides, binpkg);
+	if (dep == NULL) {
+		fprintf(stderr, "nothing provides '%s' required by '%s'\n",
+			binpkg, sourcepkg);
+		return -1;
+	}
+
+	if ((src->num_depends % 10) == 0) {
+		count = src->num_depends + 10;
+
+		new = realloc(src->depends, sizeof(src->depends[0]) * count);
+		if (new == NULL) {
+			fputs("out of memory\n", stderr);
+			return -1;
+		}
+
+		src->depends = new;
+	}
+
+	src->depends[src->num_depends++] = dep;
+	return 0;
+}
+
+static int handle_provides(const char *sourcepkg, const char *binpkg)
+{
+	source_pkg_t *src = NULL;
+
+	src = hash_table_lookup(&tbl_provides, binpkg);
+	if (src != NULL) {
+		fprintf(stderr, "%s: package already provided by %s\n",
+			binpkg, src->name);
+		return -1;
+	}
+
+	src = hash_table_lookup(&tbl_sourcepkgs, sourcepkg);
+
+	if (src == NULL) {
+		src = calloc(1, sizeof(*src));
+		if (src == NULL)
+			goto fail_oom;
+
+		src->name = strdup(sourcepkg);
+		if (src->name == NULL)
+			goto fail_oom;
+
+		if (hash_table_set(&tbl_sourcepkgs, sourcepkg, src))
+			goto fail;
+	}
+
+	return hash_table_set(&tbl_provides, binpkg, src);
+fail_oom:
+	fputs("out of memory\n", stderr);
+fail:
+	if (src != NULL)
+		free(src->name);
+	free(src);
+	return -1;
+}
+
+/*****************************************************************************/
+
+static const struct option long_opts[] = {
+	{ "provides", no_argument, NULL, 'p' },
+	{ "depends", no_argument, NULL, 'd' },
+	{ NULL, 0, NULL, 0 },
+};
+
+static const char *short_opts = "p:d:";
+
+static int process_args(int argc, char **argv)
+{
+	const char *provides = NULL, *depends = NULL;
+	int i;
+
+	for (;;) {
+		i = getopt_long(argc, argv, short_opts, long_opts, NULL);
+		if (i == -1)
+			break;
+
+		switch (i) {
+		case 'p':
+			provides = optarg;
+			break;
+		case 'd':
+			depends = optarg;
+			break;
+		default:
+			goto fail_arg;
+		}
+	}
+
+	if (optind >= argc) {
+		fputs("no packages specified\n", stderr);
+		goto fail_arg;
+	}
+
+	if (provides == NULL) {
+		fputs("no source package provides specified\n", stderr);
+		goto fail_arg;
+	}
+
+	if (hash_table_init(&tbl_provides, 1024))
+		return EXIT_FAILURE;
+
+	if (hash_table_init(&tbl_sourcepkgs, 1024))
+		goto fail_provides;
+
+	if (foreach_line(provides, handle_provides))
+		goto fail_srcpkg;
+
+	if (depends != NULL && foreach_line(depends, handle_depends) != 0)
+		goto fail_srcpkg;
+
+	return 0;
+fail_srcpkg:
+	hash_table_cleanup(&tbl_sourcepkgs);
+fail_provides:
+	hash_table_cleanup(&tbl_provides);
+	return -1;
+fail_arg:
+	tell_read_help(argv[0]);
+	return -1;
+}
+
+static void pkg_mark_deps(source_pkg_t *pkg)
+{
+	size_t i;
+
+	if (pkg->flags & FLAG_BUILD_PKG)
+		return;
+
+	pkg->flags |= FLAG_BUILD_PKG;
+
+	for (i = 0; i < pkg->num_depends; ++i) {
+		if ((pkg->depends[i]->flags & FLAG_BUILD_PKG) == 0)
+			pkg_mark_deps(pkg->depends[i]);
+	}
+}
+
+static int remove_untagged(void *usr, const char *name, void *p)
+{
+	int mask = *((int *)usr);
+	source_pkg_t *pkg = p;
+	(void)name;
+
+	if ((pkg->flags & mask) == 0) {
+		free(pkg->name);
+		free(pkg->depends);
+		free(pkg);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int remove_unmarked_deps(void *usr, const char *name, void *p)
+{
+	source_pkg_t *pkg = p;
+	size_t i = 0;
+	(void)usr; (void)name;
+
+	while (i < pkg->num_depends) {
+		if ((pkg->depends[i]->flags & FLAG_BUILD_PKG) == 0) {
+			pkg->depends[i] = pkg->depends[pkg->num_depends - 1];
+			pkg->num_depends -= 1;
+		} else {
+			++i;
+		}
+	}
+
+	return 0;
+}
+
+static int find_no_dep(void *usr, const char *name, void *p)
+{
+	source_pkg_t *pkg = p;
+	int *found = usr;
+
+	if (pkg->num_depends == 0) {
+		printf("%s\n", name);
+		pkg->flags &= ~FLAG_BUILD_PKG;
+		*found = 1;
+	}
+
+	return 0;
+}
+
+static int cmd_buildstrategy(int argc, char **argv)
+{
+	int i, ret = EXIT_FAILURE;
+	source_pkg_t *pkg;
+
+	if (process_args(argc, argv))
+		return EXIT_FAILURE;
+
+	for (i = optind; i < argc; ++i) {
+		pkg = hash_table_lookup(&tbl_provides, argv[i]);
+
+		if (pkg == NULL) {
+			fprintf(stderr, "nothing provides '%s'\n", argv[i]);
+			goto out;
+		}
+
+		pkg_mark_deps(pkg);
+	}
+
+	i = FLAG_BUILD_PKG;
+	hash_table_foreach(&tbl_sourcepkgs, &i, remove_untagged);
+
+	while (tbl_sourcepkgs.count > 0) {
+		i = 0;
+		hash_table_foreach(&tbl_sourcepkgs, &i, find_no_dep);
+		if (!i) {
+			fputs("cycle detected in package dependencies!\n",
+			      stderr);
+			goto out;
+		}
+
+		hash_table_foreach(&tbl_sourcepkgs, NULL, remove_unmarked_deps);
+
+		i = FLAG_BUILD_PKG;
+		hash_table_foreach(&tbl_sourcepkgs, &i, remove_untagged);
+	}
+
+	ret = EXIT_SUCCESS;
+out:
+	i = 0;
+	hash_table_foreach(&tbl_sourcepkgs, &i, remove_untagged);
+	hash_table_cleanup(&tbl_sourcepkgs);
+	hash_table_cleanup(&tbl_provides);
+	return ret;
+}
+
+static command_t buildstrategy = {
+	.cmd = "buildstrategy",
+	.usage = "[OPTIONS...] <packages>",
+	.s_desc = "work out what source packages to build in what order",
+	.l_desc =
+"The buildstrategy command takes as input a description of what binary\n"
+"packages a source package needs in order to build and what binary packages\n"
+"in turn produces in the process. The command then takes from the command\n"
+"line arguments a list of desired binary packages and works out a minimal\n"
+"set of source packages to build and in what order they should be built.\n"
+"\n"
+"Possible options:\n"
+"  --provides, -p <file>  A two column CSV file. Each line contains the name\n"
+"                         of a source package and a binary package that it\n"
+"                         produces when built. If a source packages provides\n"
+"                         multiple binary packages, use one line for each\n"
+"                         binary package.\n"
+"  --depends, -d <file>   A two column CSV file. Each line contains the name\n"
+"                         of a source package and a binary package that it\n"
+"                         requires to build.\n",
+	.run_cmd = cmd_buildstrategy,
+};
+
+REGISTER_COMMAND(buildstrategy)
diff --git a/main/cmd/buildstrategy/buildstrategy.h b/main/cmd/buildstrategy/buildstrategy.h
new file mode 100644
index 0000000..56ad229
--- /dev/null
+++ b/main/cmd/buildstrategy/buildstrategy.h
@@ -0,0 +1,27 @@
+#ifndef BUILDSTRATEGY_H
+#define BUILDSTRATEGY_H
+
+#include <getopt.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdio.h>
+#include <errno.h>
+
+#include "command.h"
+#include "util/hashtable.h"
+
+enum {
+	FLAG_BUILD_PKG = 0x01,
+};
+
+typedef struct source_pkg_t {
+	char *name;
+
+	struct source_pkg_t **depends;
+	size_t num_depends;
+
+	int flags;
+} source_pkg_t;
+
+#endif /* BUILDSTRATEGY_H */