diff --git a/pipsi/__init__.py b/pipsi/__init__.py
index 470ce58..696c64f 100644
--- a/pipsi/__init__.py
+++ b/pipsi/__init__.py
@@ -423,6 +423,17 @@ def upgrade(self, package, editable=False):
 
         return True
 
+    def upgrade_all(self, packages, editable=False):
+        if not packages:
+            if os.path.isdir(self.home):
+                all_installed_packages = os.listdir(self.home)
+                packages = all_installed_packages
+
+        for package in packages:
+            self.upgrade(package, editable)
+
+        return True
+
     def list_everything(self, versions=False):
         venvs = {}
         python = '/Scripts/python.exe' if IS_WIN else '/bin/python'
@@ -491,14 +502,14 @@ def install(repo, package, python, editable, system_site_packages):
 
 
 @cli.command()
-@click.argument('package')
+@click.argument('packages', required=False, nargs=-1)
 @click.option('--editable', '-e', is_flag=True,
               help='Enable editable installation.  This only works for '
                    'locally installed packages.')
 @click.pass_obj
-def upgrade(repo, package, editable):
-    """Upgrades an already installed package."""
-    if repo.upgrade(package, editable):
+def upgrade(repo, packages, editable):
+    """Upgrades the specifiled (or all) already installed packages."""
+    if repo.upgrade_all(packages, editable):
         click.echo('Done.')
     else:
         sys.exit(1)
diff --git a/testing/test_repo.py b/testing/test_repo.py
index 90e17cf..9349bf0 100644
--- a/testing/test_repo.py
+++ b/testing/test_repo.py
@@ -1,8 +1,10 @@
 import os
 import sys
+import subprocess
 import pytest
 import click
-from pipsi import Repo, find_scripts
+from click.testing import CliRunner
+from pipsi import Repo, find_scripts, cli
 
 
 @pytest.fixture
@@ -60,6 +62,43 @@ def test_simple_install(repo, home, bin, package, glob):
     assert repo.upgrade(package)
 
 
+def test_upgrade_all(repo, home, bin):
+    def installed_version(package):
+        pip_freeze = ['%s/%s/bin/pip' % (home.strpath, package), 'freeze']
+        frozen_requirements = subprocess.check_output(pip_freeze, stderr=subprocess.STDOUT)
+        frozen_requirements = frozen_requirements.strip()
+        for requirement in frozen_requirements.split('\n'):
+            name, version = requirement.split('==', 2)
+            if name == bytes(package):
+                version_as_tuple = tuple([int(i) for i in version.split('.')])
+                return version_as_tuple
+
+    arbitrary_packages = [
+        ('grin', (1, 2)),
+        ('curlish', (1, 17)),
+    ]
+
+    # Install packages and assert given versions were installed:
+    for name, version_tuple in arbitrary_packages:
+        package = '%s==%s' % (name, '.'.join([str(i) for i in version_tuple]))
+        assert repo.install(package)
+        assert installed_version(name) == version_tuple
+
+    # Run upgrade command with no packages as arguments:
+    runner = CliRunner()
+    args = ['--home', str(home),
+            '--bin-dir', str(bin),
+            'upgrade',
+             # Note: no packages are given as arguments!
+            ]
+    result = runner.invoke(cli, args)
+    assert result.exit_code == 0
+
+    # Assert versions have increased:
+    for name, version_tuple in arbitrary_packages:
+        assert installed_version(name) > version_tuple
+
+
 @pytest.mark.xfail(
     sys.version_info[0] != 3,
     reason='attic is python3 only', run=False)