diff --git a/examples/vhdl/submodule/run.py b/examples/vhdl/submodule/run.py
new file mode 100644
index 000000000..3c14f7a4d
--- /dev/null
+++ b/examples/vhdl/submodule/run.py
@@ -0,0 +1,34 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+#
+# Copyright (c) 2014-2019, Lars Asplund lars.anders.asplund@gmail.com
+
+"""
+Submodule support
+-------------
+This script shows how to import smaller submodules in a bigger design. 
+
+The submodules contains a own run.py script in which the sources are defined.
+With 'add_submodule' you can add the complete project into your top design.
+Usecase could be a CPU design which uses some periphery which is managed in 
+seperate projects.
+"""
+
+from os.path import join, dirname
+from vunit import VUnit
+
+root = dirname(__file__)
+
+vu = VUnit.from_argv()
+
+vu.add_json4vhdl()
+
+lib = vu.add_library("lib")
+lib.add_source_files(join(root, "src/*.vhd"))
+lib.add_source_files(join(root, "tb/*.vhd"))
+
+vu.add_submodule('src/adder/run.py')
+
+if __name__ == '__main__':
+    vu.main()
diff --git a/examples/vhdl/submodule/src/adder/run.py b/examples/vhdl/submodule/src/adder/run.py
new file mode 100644
index 000000000..774132adf
--- /dev/null
+++ b/examples/vhdl/submodule/src/adder/run.py
@@ -0,0 +1,29 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+#
+# Copyright (c) 2014-2019, Lars Asplund lars.anders.asplund@gmail.com
+
+"""
+Submodule support
+-------------
+
+This is only a small example and shows how a complete vunit design can be 
+imported at once. Intended use case could be a seperately managed periphery
+which gets imported in a bigger top design like a CPU or complete vhdl librarys.
+"""
+
+from os.path import join, dirname
+from vunit import VUnit
+
+root = dirname(__file__)
+
+vu = VUnit.from_argv()
+
+vu.add_json4vhdl()
+
+lib = vu.add_library("adder")
+lib.add_source_files(join(root, "src/*.vhd"))
+
+if __name__ == '__main__':
+    vu.main()
diff --git a/examples/vhdl/submodule/src/adder/src/adder.vhd b/examples/vhdl/submodule/src/adder/src/adder.vhd
new file mode 100644
index 000000000..9df1b5f23
--- /dev/null
+++ b/examples/vhdl/submodule/src/adder/src/adder.vhd
@@ -0,0 +1,30 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at http://mozilla.org/MPL/2.0/.
+--
+-- Copyright (c) 2014-2019, Lars Asplund lars.anders.asplund@gmail.com
+
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+entity adder is
+  generic (
+      BITS : positive);
+  port(
+    clk : in std_logic;
+    op_a : in unsigned(BITS - 1 downto 0);
+    op_b : in unsigned(BITS - 1 downto 0);
+    sum : out unsigned(BITS - 1 downto 0)
+  );
+end entity;
+
+architecture arch of adder is
+begin
+  main : process(clk)
+  begin
+    if rising_edge(clk) then
+        sum <= op_a + op_b;
+    end if;
+  end process;
+end architecture;
diff --git a/examples/vhdl/submodule/src/top.vhd b/examples/vhdl/submodule/src/top.vhd
new file mode 100644
index 000000000..43f87628c
--- /dev/null
+++ b/examples/vhdl/submodule/src/top.vhd
@@ -0,0 +1,38 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at http://mozilla.org/MPL/2.0/.
+--
+-- Copyright (c) 2014-2019, Lars Asplund lars.anders.asplund@gmail.com
+
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+library adder;
+
+entity top is
+  generic (
+      BITS : positive);
+  port(
+    clk : in std_logic;
+    op_a : in unsigned(BITS - 1 downto 0);
+    op_b : in unsigned(BITS - 1 downto 0);
+    sum : out unsigned(BITS - 1 downto 0)
+  );
+end entity;
+
+architecture arch of top is
+begin
+
+  adder_inst: entity adder.adder
+    generic map(
+      BITS => BITS
+    )
+    port map(
+      clk => clk,
+      op_a => op_a,
+      op_b => op_b,
+      sum => sum
+    );
+
+end architecture;
diff --git a/examples/vhdl/submodule/tb/top_tb.vhd b/examples/vhdl/submodule/tb/top_tb.vhd
new file mode 100644
index 000000000..b4f6d2396
--- /dev/null
+++ b/examples/vhdl/submodule/tb/top_tb.vhd
@@ -0,0 +1,55 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at http://mozilla.org/MPL/2.0/.
+--
+-- Copyright (c) 2014-2019, Lars Asplund lars.anders.asplund@gmail.com
+
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+library vunit_lib;
+context vunit_lib.vunit_context;
+
+entity top_tb is
+  generic (
+    RUNNER_CFG	: string);
+end entity;
+
+architecture arch of top_tb is
+  signal clk : std_logic := '0';
+
+  constant BITS : natural := 8;
+  signal in_a, in_b, add_out : unsigned(BITS - 1 downto 0);
+
+begin
+  clk <= not clk after 1 ns;
+
+
+  main: process
+  begin
+    test_runner_setup(runner, runner_cfg);
+    while test_suite loop
+      if run("test") then
+        in_a <= to_unsigned(10, in_a);
+        in_b <= to_unsigned(15, in_b);
+        wait for 3 ns;
+        check(add_out = in_a + in_b, "Addition failed");
+      end if;
+    end loop;
+    test_runner_cleanup(runner);
+    wait;
+  end process;
+
+  top_module: entity work.top
+  generic map(
+    BITS => BITS
+  )
+  port map(
+    clk => clk,
+    op_a => in_a,
+    op_b => in_b,
+    sum => add_out
+  );
+  
+end architecture;
diff --git a/vunit/ui.py b/vunit/ui.py
index 73520f2f8..c146f5501 100644
--- a/vunit/ui.py
+++ b/vunit/ui.py
@@ -251,6 +251,7 @@
 from os.path import exists, abspath, join, basename, splitext, normpath, dirname
 from glob import glob
 from fnmatch import fnmatch
+import importlib
 from vunit.database import PickledDataBase, DataBase
 from vunit import ostools
 from vunit.vunit_cli import VUnitCLI
@@ -288,6 +289,13 @@ class VUnit(object):  # pylint: disable=too-many-instance-attributes, too-many-p
 
        from vunit import VUnit
     """
+    _instance = None
+    _initialized = False
+    def __new__(cls, *args, **kwargs):
+        if not cls._instance:
+            cls._instance = super(VUnit, cls).__new__(cls)
+        
+        return cls._instance
 
     @classmethod
     def from_argv(cls, argv=None, compile_builtins=True, vhdl_standard=None):
@@ -325,6 +333,9 @@ def from_args(cls, args, compile_builtins=True, vhdl_standard=None):
         return cls(args, compile_builtins=compile_builtins, vhdl_standard=vhdl_standard)
 
     def __init__(self, args, compile_builtins=True, vhdl_standard=None):
+        if self._initialized != False:
+            return
+
         self._args = args
         self._configure_logging(args.log_level)
         self._output_path = abspath(args.output_path)
@@ -346,6 +357,9 @@ def test_filter(name, attribute_names):
 
         self._test_filter = test_filter
         self._vhdl_standard = select_vhdl_standard(vhdl_standard)
+        self._import_submodule = False
+        self._import_submodule_latch = False
+        self._import_testbenches = True
 
         self._external_preprocessors = []
         self._location_preprocessor = None
@@ -374,6 +388,8 @@ def test_filter(name, attribute_names):
         if compile_builtins:
             self.add_builtins()
 
+        self._initialized = True
+
     def _create_database(self):
         """
         Create a persistent database to store expensive parse results
@@ -490,6 +506,8 @@ def add_library(self, library_name, vhdl_standard=None, allow_duplicate=False):
         path = join(self._simulator_output_path, "libraries", library_name)
         if not self._project.has_library(library_name):
             self._project.add_library(library_name, abspath(path), vhdl_standard)
+        elif self._import_submodule:
+            pass
         elif not allow_duplicate:
             raise ValueError("Library %s already added. Use allow_duplicate to ignore this error." % library_name)
         return self.library(library_name)
@@ -1141,6 +1159,27 @@ def get_implementation_subset(self, source_files):
         return SourceFileList([SourceFile(source_file, self._project, self)
                                for source_file in source_files])
 
+    def add_submodule(self, module, import_testbenches = False):
+        """
+        Add a complete vunit build script to the design at once. 
+        
+        :param module: Path to the submodule's run.py file
+        :param import_testbenches : If set, the submodules testbenches are imported, otherwise not.
+        """
+
+        f = open(module) # raises FileNotFoundError if the module is not available
+        rootpath = os.getcwd()
+        path = os.path.abspath(os.path.dirname(module))
+        sys.path.insert(0, path)
+        os.chdir(path)
+        self._import_submodule = True
+        self._import_submodule_latch = True
+        self._import_testbenches = import_testbenches
+        importlib.import_module(os.path.basename(module).split('.')[0])
+        self._import_testbenches = True
+        self._import_submodule = False
+        os.chdir(rootpath)
+        sys.path.remove(path)
 
 class Library(object):
     """
@@ -1350,6 +1389,13 @@ def add_source_file(self,  # pylint: disable=too-many-arguments
         new_file_name = self._parent._preprocess(  # pylint: disable=protected-access
             self._library_name, file_name, preprocessors)
 
+        if self._parent._import_submodule_latch:
+            try:
+                duplicate = self.get_source_file('*/' + os.path.basename(file_name))
+                return duplicate
+            except ValueError:
+                pass
+
         source_file = self._project.add_source_file(new_file_name,
                                                     self._library_name,
                                                     file_type=file_type,
@@ -1360,7 +1406,8 @@ def add_source_file(self,  # pylint: disable=too-many-arguments
         # To get correct tb_path generic
         source_file.original_name = file_name
 
-        self._test_bench_list.add_from_source_file(source_file)
+        if self._parent._import_testbenches:
+            self._test_bench_list.add_from_source_file(source_file)
 
         return SourceFile(source_file,
                           self._project,