diff --git a/IPython/core/extensions.py b/IPython/core/extensions.py
index 0298a8f..f7602dd 100644
--- a/IPython/core/extensions.py
+++ b/IPython/core/extensions.py
@@ -19,6 +19,8 @@ Authors:
 
 import os
 import sys
+from urllib import urlretrieve
+from urlparse import urlparse
 
 from IPython.config.configurable import Configurable
 from IPython.utils.traitlets import Instance
@@ -123,3 +125,22 @@ class ExtensionManager(Configurable):
     def _call_unload_ipython_extension(self, mod):
         if hasattr(mod, 'unload_ipython_extension'):
             return mod.unload_ipython_extension(self.shell)
+    
+    def install_extension(self, url, filename=None):
+        """Download and install an IPython extension. 
+        
+        If filename is given, the file will be so named (inside the extension
+        directory). Otherwise, the name from the URL will be used. The file must
+        have a .py or .zip extension; otherwise, a ValueError will be raised.
+        """
+        # Ensure the extension directory exists
+        if not os.path.isdir(self.ipython_extension_dir):
+            os.makedirs(self.ipython_extension_dir, mode = 0777)
+        
+        if filename is None:
+            filename = urlparse(url).path.split('/')[-1]
+        if os.path.splitext(filename)[1] not in ('.py', '.zip'):
+            raise ValueError("The file must have a .py or .zip extension", filename)
+        
+        filename = os.path.join(self.ipython_extension_dir, filename)
+        return urlretrieve(url, filename)
diff --git a/IPython/core/magic.py b/IPython/core/magic.py
index 2f233fb..4996c20 100644
--- a/IPython/core/magic.py
+++ b/IPython/core/magic.py
@@ -3457,6 +3457,31 @@ Defaulting color scheme to 'NoColor'"""
             # print simple error message, rather than traceback if we can't
             # hook up the GUI
             error(str(e))
+    
+    def magic_install_ext(self, parameter_s):
+        """Download and install an extension from a URL, e.g.::
+        
+            %install_ext https://bitbucket.org/birkenfeld/ipython-physics/raw/d1310a2ab15d/physics.py
+        
+        The URL should point to an importable Python module - either a .py file
+        or a .zip file.
+        
+        Parameters:
+        
+          -n filename : Specify a name for the file, rather than taking it from
+                        the URL.
+        """
+        opts, args = self.parse_options(parameter_s, 'n:')
+        try:
+            filename, headers = self.extension_manager.install_extension(args, opts.get('n'))
+        except ValueError as e:
+            print e
+            return
+        
+        filename = os.path.basename(filename)
+        print "Installed %s. To use it, type:" % filename
+        print "  %%load_ext %s" % os.path.splitext(filename)[0]
+        
 
     def magic_load_ext(self, module_str):
         """Load an IPython extension by its module name."""