diff --git a/CHANGELOG b/CHANGELOG
index 2acbb45..5379c71 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,14 @@
+0.8.0
+    ProxyInfo objects now can construct themselves from environment
+    variables commonly-used in Unix environments. By default, the Http
+    class will construct a ProxyInfo instance based on these environment
+    variables. To achieve the previous behavior, where environment
+    variables are ignored, pass proxy_info=None to Http().
+
+    The following issues have been addressed:
+
+    Issue 159: automatic detection of proxy configuration.
+
 0.7.1
     Fix failure to install cacerts.txt for 2.x installs.
 
@@ -15,8 +26,8 @@
     Fixes issue 72. Always lowercase authorization header.
     Fix issue 47. Redirects that become a GET should not have a body.
     Fixes issue 19. Set Content-location on redirected HEAD requests
-    Fixes issue 139. Redirect with a GET on 302 regardless of the originating method. 
-    Fixes issue 138. Handle unicode in headers when writing and retrieving cache entries. Who says headers have to be ASCII! 
+    Fixes issue 139. Redirect with a GET on 302 regardless of the originating method.
+    Fixes issue 138. Handle unicode in headers when writing and retrieving cache entries. Who says headers have to be ASCII!
     Add certificate validation. Work initially started by Christoph Kern.
     Set a version number. Fixes issue # 135.
     Sync to latest version of socks.py
@@ -32,14 +43,14 @@
 
    The following issues have been addressed:
 
-    #51 - Failure to handle server legitimately closing connection before request body is fully sent	
-    #77 - Duplicated caching test	 
+    #51 - Failure to handle server legitimately closing connection before request body is fully sent
+    #77 - Duplicated caching test
     #65 - Transform _normalize_headers into a method of Http class
-    #45 - Vary header	  
-    #73 - All files in Mercurial are executable	 
-    #81 - Have a useful .hgignore	 	 
-    #78 - Add release tags to the Mercurial repository		 
-    #67 - HEAD requests cause next request to be retried	  
+    #45 - Vary header
+    #73 - All files in Mercurial are executable
+    #81 - Have a useful .hgignore
+    #78 - Add release tags to the Mercurial repository
+    #67 - HEAD requests cause next request to be retried
 
    Mostly bug fixes, the big enhancement is the addition of proper Vary: header
    handling. Thanks to Chris Dent for that change.
@@ -53,7 +64,7 @@
 
    Fixed the following bugs:
 
-      #12 - Cache-Control: only-if-cached incorrectly does request if item not in cache 
+      #12 - Cache-Control: only-if-cached incorrectly does request if item not in cache
       #39 - Deprecation warnings in Python 2.6
       #54 - Http.request fails accesing Google account via http proxy
       #56 - Block on response.read() for HEAD requests.
@@ -66,13 +77,13 @@
 
    Added support for proxies if the Socksipy module is installed.
 
-   Fixed bug with some HEAD responses having content-length set to 
+   Fixed bug with some HEAD responses having content-length set to
    zero incorrectly.
 
    Fixed most except's to catch a specific exception.
 
    Added 'connection_type' parameter to Http.request().
- 
+
    The default for 'force_exception_to_status_code' was changed to False. Defaulting
    to True was causing quite a bit of confusion.
 
@@ -89,11 +100,11 @@
 
    Many improvements to the file cache:
 
-     1.  The names in the cache are now much less 
+     1.  The names in the cache are now much less
          opaque, which should help with debugging.
 
-     2.  The disk cache is now Apache mod_asis compatible. 
-     
+     2.  The disk cache is now Apache mod_asis compatible.
+
      3.  A Content-Location: header is supplied and stored in the
          cache which points to the original requested URI.
 
@@ -106,7 +117,7 @@
    Http.add_credentials() now takes an optional domain to restrict
    the credentials to being only used on that domain.
 
-   Added Http.add_certificate() which allows setting 
+   Added Http.add_certificate() which allows setting
    a key and cert for SSL connnections.
 
    Many other bugs fixed.
@@ -115,17 +126,17 @@
 0.2.0
    Added support for Google Auth.
 
-   Added experimental support for HMACDigest.  
+   Added experimental support for HMACDigest.
 
    Added support for a pluggable caching system. Now supports
    the old system of using the file system and now memcached.
 
-   Added httplib2.debuglevel which turns on debugging. 
+   Added httplib2.debuglevel which turns on debugging.
 
    Change Response._previous to Response.previous.
 
    Addded Http.follow_all_redirects which forces
-   httplib2 to follow all redirects, as opposed to 
+   httplib2 to follow all redirects, as opposed to
    following only the safe redirects. This makes the
    GData protocol easier to use.
 
@@ -140,12 +151,12 @@
     4. Subsequent requests to resources that had timed out would raise an exception.
     And one feature request for 'method' to default to GET.
 
-    Xavier Verges Farrero supplied what I needed to make the 
+    Xavier Verges Farrero supplied what I needed to make the
     library work with Python 2.3.
 
     I added distutils based setup.py.
 
-0.1 Rev 86 
-    
+0.1 Rev 86
+
     Initial Release
 
diff --git a/python2/httplib2/__init__.py b/python2/httplib2/__init__.py
index ce153d6..b1b882a 100644
--- a/python2/httplib2/__init__.py
+++ b/python2/httplib2/__init__.py
@@ -776,7 +776,7 @@
     @classmethod
     def from_url(cls, url, method='http'):
         """
-        Construct a ProxyInfo from a URL
+        Construct a ProxyInfo from a URL (such as http_proxy env var)
         """
         url = urlparse.urlparse(url)
         ident, sep, host_port = url.netloc.rpartition('@')
@@ -795,6 +795,9 @@
             proxy_pass = password or None,
         )
 
+    def applies_to(self, hostname):
+        return hostname not in self.bypass_hosts
+
 
 class HTTPConnectionWithTimeout(httplib.HTTPConnection):
     """
@@ -1088,11 +1091,10 @@
 
 and more.
     """
-    def __init__(self, cache=None, timeout=None, proxy_info=None,
+    def __init__(self, cache=None, timeout=None,
+                 proxy_info=ProxyInfo.from_environment,
                  ca_certs=None, disable_ssl_certificate_validation=False):
         """
-        The value of proxy_info is a ProxyInfo instance.
-
         If 'cache' is a string then it is used as a directory name for
         a disk cache. Otherwise it must be an object that supports the
         same interface as FileCache.
@@ -1102,6 +1104,13 @@
         for example the docs of socket.setdefaulttimeout():
         http://docs.python.org/library/socket.html#socket.setdefaulttimeout
 
+        `proxy_info` may be:
+          - a callable that takes the http scheme ('http' or 'https') and
+            returns a ProxyInfo instance per request. By default, uses
+            ProxyInfo.from_environment.
+          - a ProxyInfo instance (static proxy config).
+          - None (proxy disabled).
+
         ca_certs is the path of a file containing root CA certificates for SSL
         server certificate validation.  By default, a CA cert file bundled with
         httplib2 is used.
@@ -1349,6 +1358,8 @@
                 scheme = 'https'
                 authority = domain_port[0]
 
+            proxy_info = self._get_proxy_info(scheme, authority)
+
             conn_key = scheme+":"+authority
             if conn_key in self.connections:
                 conn = self.connections[conn_key]
@@ -1361,21 +1372,21 @@
                         conn = self.connections[conn_key] = connection_type(
                                 authority, key_file=certs[0][0],
                                 cert_file=certs[0][1], timeout=self.timeout,
-                                proxy_info=self.proxy_info,
+                                proxy_info=proxy_info,
                                 ca_certs=self.ca_certs,
                                 disable_ssl_certificate_validation=
                                         self.disable_ssl_certificate_validation)
                     else:
                         conn = self.connections[conn_key] = connection_type(
                                 authority, timeout=self.timeout,
-                                proxy_info=self.proxy_info,
+                                proxy_info=proxy_info,
                                 ca_certs=self.ca_certs,
                                 disable_ssl_certificate_validation=
                                         self.disable_ssl_certificate_validation)
                 else:
                     conn = self.connections[conn_key] = connection_type(
                             authority, timeout=self.timeout,
-                            proxy_info=self.proxy_info)
+                            proxy_info=proxy_info)
                 conn.set_debuglevel(debuglevel)
 
             if 'range' not in headers and 'accept-encoding' not in headers:
@@ -1521,6 +1532,18 @@
 
         return (response, content)
 
+    def _get_proxy_info(self, scheme, authority):
+        """Return a ProxyInfo instance (or None) based on the scheme
+        and authority.
+        """
+        proxy_info = self.proxy_info
+        if callable(proxy_info):
+            proxy_info = proxy_info(scheme)
+
+        if (hasattr(proxy_info, 'applies_to')
+            and not proxy_info.applies_to(authority)):
+            proxy_info = None
+        return proxy_info
 
 
 class Response(dict):
diff --git a/python2/httplib2test.py b/python2/httplib2test.py
index bcfc073..705cc38 100755
--- a/python2/httplib2test.py
+++ b/python2/httplib2test.py
@@ -1596,6 +1596,14 @@
         pi = httplib2.ProxyInfo.from_environment()
         self.assertEquals(pi, None)
 
+    def test_applies_to(self):
+        os.environ['http_proxy'] = 'http://myproxy.example.com:80'
+        os.environ['https_proxy'] = 'http://myproxy.example.com:81'
+        os.environ['no_proxy'] = 'localhost,otherhost.domain.local'
+        pi = httplib2.ProxyInfo.from_environment()
+        self.assertFalse(pi.applies_to('localhost'))
+        self.assertTrue(pi.applies_to('www.google.com'))
+
 
 if __name__ == '__main__':
     unittest.main()