diff --git a/jedi/_compatibility.py b/jedi/_compatibility.py
index 52a20fe2..3481e52a 100644
--- a/jedi/_compatibility.py
+++ b/jedi/_compatibility.py
@@ -289,3 +289,25 @@ def utf8_repr(func):
         return func
     else:
         return wrapper
+
+
+try:
+    from subprocess import check_output
+except ImportError:
+    def check_output(*popenargs, **kwargs):
+        """
+        Taken from Python 2.6.
+        """
+        from subprocess import Popen, PIPE, CalledProcessError
+
+        if 'stdout' in kwargs:
+            raise ValueError('stdout argument not allowed, it will be overridden.')
+        process = Popen(stdout=PIPE, *popenargs, **kwargs)
+        output, unused_err = process.communicate()
+        retcode = process.poll()
+        if retcode:
+            cmd = kwargs.get("args")
+            if cmd is None:
+                cmd = popenargs[0]
+            raise CalledProcessError(retcode, cmd, output=output)
+        return output
diff --git a/jedi/api/virtualenv.py b/jedi/api/virtualenv.py
new file mode 100644
index 00000000..d2043b20
--- /dev/null
+++ b/jedi/api/virtualenv.py
@@ -0,0 +1,106 @@
+import os
+import re
+import sysconfig
+from subprocess import CalledProcessError
+from collections import namedtuple
+
+from jedi._compatibility import check_output
+from jedi.evaluate.project import Project
+from jedi.cache import memoize_method
+
+
+_VersionInfo = namedtuple('VersionInfo', 'major minor micro')
+
+
+class NoVirtualEnv(Exception):
+    pass
+
+
+class Environment(object):
+    def __init__(self, path, executable):
+        self._path = path
+        self._executable = executable
+        self.version_info = _get_version(self._executable)
+
+    def __repr__(self):
+        return '<%s: %s>' % (self.__class__.__name__, self._path)
+
+    def get_project(self):
+        return Project(self.get_sys_path())
+
+    def get_sys_path(self):
+        vars = {
+            'base': self._path
+        }
+        lib_path = sysconfig.get_path('stdlib', vars=vars)
+        # It's pretty much impossible to generate the sys path without actually
+        # executing Python. The sys path (when starting with -S) itself depends
+        # on how the Python version was compiled (ENV variables).
+        # If you omit -S when starting Python (normal case), additionally
+        # site.py gets executed.
+        write
+
+        # venv
+        ['', '/usr/lib/python3.3', '/usr/lib/python3.3/plat-x86_64-linux-gnu',
+         '/usr/lib/python3.3/lib-dynload',
+         '/home/dave/source/python/virtenv/venv3.3/lib/python3.3/site-packages']
+
+        ['/usr/lib/python3.4', '/usr/lib/python3.4/plat-x86_64-linux-gnu',
+         '/usr/lib/python3.4/lib-dynload',
+         '/home/dave/source/stuff_cloudscale/rgw-metrics/venv/lib/python3.4/site-packages']
+
+        ['', '/usr/lib/python35.zip', '/usr/lib/python3.5',
+         '/usr/lib/python3.5/plat-x86_64-linux-gnu',
+         '/usr/lib/python3.5/lib-dynload',
+         '/home/dave/source/python/virtenv/venv3.5/lib/python3.5/site-packages']
+
+
+        {'purelib': '{base}/local/lib/python{py_version_short}/dist-packages',
+         'stdlib': '{base}/lib/python{py_version_short}',
+         'scripts': '{base}/local/bin',
+         'platinclude': '{platbase}/local/include/python{py_version_short}',
+         'include': '{base}/local/include/python{py_version_short}',
+         'data': '{base}/local',
+         'platstdlib': '{platbase}/lib/python{py_version_short}',
+         'platlib': '{platbase}/local/lib/python{py_version_short}/dist-packages'}
+        return [] + additional_paths
+
+    def _get_long_running_process(self):
+        return process
+
+
+def find_virtualenvs(paths=None):
+    if paths is None:
+        paths = []
+
+    for path in paths:
+        executable = _get_executable_path(path)
+        try:
+            yield Environment(path, executable)
+        except NoVirtualEnv:
+            pass
+
+
+def _get_executable_path(path):
+    """
+    Returns None if it's not actually a virtual env.
+    """
+    bin_folder = os.path.join(path, 'bin')
+    activate = os.path.join(bin_folder, 'activate')
+    python = os.path.join(bin_folder, 'python')
+    if not all(os.path.exists(p) for p in (activate, python)):
+        return None
+    return python
+
+
+def _get_version(executable):
+    try:
+        output = check_output(executable, '--version')
+    except (CalledProcessError, OSError):
+        raise NoVirtualEnv()
+
+    match = re.match(r'Python (\d+)\.(\d+)\.(\d+)', output)
+    if match is None:
+        raise NoVirtualEnv()
+
+    return _VersionInfo(*match.groups())
diff --git a/jedi/evaluate/project.py b/jedi/evaluate/project.py
index b90f0f0c..fe3fb5d7 100644
--- a/jedi/evaluate/project.py
+++ b/jedi/evaluate/project.py
@@ -2,7 +2,7 @@ import os
 import sys
 
 from jedi.evaluate.sys_path import get_venv_path, detect_additional_paths
-from jedi.cache import underscore_memoization
+from jedi.cache import memoize_method
 
 
 class Project(object):
@@ -32,7 +32,7 @@ class Project(object):
         self._evaluator = evaluator
 
     @property
-    @underscore_memoization
+    @memoize_method
     def sys_path(self):
         if self._script_path is None:
             return self._base_sys_path
diff --git a/jedi/evaluate/site.py b/jedi/evaluate/site.py
index bf884fae..de9443f2 100644
--- a/jedi/evaluate/site.py
+++ b/jedi/evaluate/site.py
@@ -17,6 +17,7 @@ from __future__ import print_function
 
 import sys
 import os
+from sysconfig import get_config_var
 
 
 def makepath(*paths):
@@ -108,3 +109,8 @@ def addsitedir(sys_path, sitedir, known_paths=None):
     if reset:
         known_paths = None
     return known_paths
+
+
+def getuserbase():
+    """Returns the `user base` directory path."""
+    return get_config_var('userbase')