diff --git a/AUTHORS b/AUTHORS
index d3244dfe3..3f43c7479 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -143,6 +143,7 @@ Ned Batchelder
 Neven Mundar
 Nicolas Delaby
 Oleg Pidsadnyi
+Oleg Sushchenko
 Oliver Bestwalter
 Omar Kohl
 Omer Hadari
diff --git a/_pytest/config.py b/_pytest/config.py
index d97771155..a9b071b6f 100644
--- a/_pytest/config.py
+++ b/_pytest/config.py
@@ -991,7 +991,8 @@ class Config(object):
 
     def _initini(self, args):
         ns, unknown_args = self._parser.parse_known_and_unknown_args(args, namespace=self.option.copy())
-        r = determine_setup(ns.inifilename, ns.file_or_dir + unknown_args, warnfunc=self.warn)
+        r = determine_setup(ns.inifilename, ns.file_or_dir + unknown_args, warnfunc=self.warn,
+                            rootdir_cmd_arg=ns.rootdir or None)
         self.rootdir, self.inifile, self.inicfg = r
         self._parser.extra_info['rootdir'] = self.rootdir
         self._parser.extra_info['inifile'] = self.inifile
@@ -1323,7 +1324,7 @@ def get_dirs_from_args(args):
     ]
 
 
-def determine_setup(inifile, args, warnfunc=None):
+def determine_setup(inifile, args, warnfunc=None, rootdir_cmd_arg=None):
     dirs = get_dirs_from_args(args)
     if inifile:
         iniconfig = py.iniconfig.IniConfig(inifile)
@@ -1346,6 +1347,11 @@ def determine_setup(inifile, args, warnfunc=None):
                     is_fs_root = os.path.splitdrive(str(rootdir))[1] == '/'
                     if is_fs_root:
                         rootdir = ancestor
+    if rootdir_cmd_arg:
+        rootdir_abs_path = py.path.local(os.path.expandvars(rootdir_cmd_arg))
+        if not os.path.isdir(str(rootdir_abs_path)):
+            raise UsageError("Directory '{}' not found. Check your '--rootdir' option.".format(rootdir_abs_path))
+        rootdir = rootdir_abs_path
     return rootdir, inifile, inicfg or {}
 
 
diff --git a/_pytest/main.py b/_pytest/main.py
index 1caa7ff1e..f3dbd4344 100644
--- a/_pytest/main.py
+++ b/_pytest/main.py
@@ -53,6 +53,11 @@ def pytest_addoption(parser):
     group._addoption("--continue-on-collection-errors", action="store_true",
                      default=False, dest="continue_on_collection_errors",
                      help="Force test execution even if collection errors occur.")
+    group._addoption("--rootdir", action="store",
+                     dest="rootdir",
+                     help="Define root directory for tests. Can be relative path: 'root_dir', './root_dir', "
+                          "'root_dir/another_dir/'; absolute path: '/home/user/root_dir'; path with variables: "
+                          "'$HOME/root_dir'.")
 
     group = parser.getgroup("collect", "collection")
     group.addoption('--collectonly', '--collect-only', action="store_true",
@@ -283,6 +288,7 @@ class Session(nodes.FSCollector):
         self.trace = config.trace.root.get("collection")
         self._norecursepatterns = config.getini("norecursedirs")
         self.startdir = py.path.local()
+
         self.config.pluginmanager.register(self, name="session")
 
     def _makeid(self):
diff --git a/changelog/1642.trivial b/changelog/1642.trivial
new file mode 100644
index 000000000..a6acc5565
--- /dev/null
+++ b/changelog/1642.trivial
@@ -0,0 +1 @@
+Add ``--rootdir`` command-line option to override the rules for discovering the root directory. See `customize <https://docs.pytest.org/en/latest/customize.html>`_ in the documentation for details.
diff --git a/doc/en/customize.rst b/doc/en/customize.rst
index 9fe094ba1..f819c5974 100644
--- a/doc/en/customize.rst
+++ b/doc/en/customize.rst
@@ -38,6 +38,10 @@ Here's a summary what ``pytest`` uses ``rootdir`` for:
 Important to emphasize that ``rootdir`` is **NOT** used to modify ``sys.path``/``PYTHONPATH`` or
 influence how modules are imported. See :ref:`pythonpath` for more details.
 
+``--rootdir=path`` command-line option can be used to force a specific directory. 
+The directory passed may contain environment variables when it is used in conjunction
+with ``addopts`` in a ``pytest.ini`` file.
+
 Finding the ``rootdir``
 ~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/testing/test_session.py b/testing/test_session.py
index 9ec13f523..68534b102 100644
--- a/testing/test_session.py
+++ b/testing/test_session.py
@@ -1,4 +1,5 @@
 from __future__ import absolute_import, division, print_function
+
 import pytest
 
 from _pytest.main import EXIT_NOTESTSCOLLECTED
@@ -253,3 +254,32 @@ def test_sessionfinish_with_start(testdir):
     """)
     res = testdir.runpytest("--collect-only")
     assert res.ret == EXIT_NOTESTSCOLLECTED
+
+
+@pytest.mark.parametrize("path", ["root", "{relative}/root", "{environment}/root"])
+def test_rootdir_option_arg(testdir, monkeypatch, path):
+    monkeypatch.setenv('PY_ROOTDIR_PATH', str(testdir.tmpdir))
+    path = path.format(relative=str(testdir.tmpdir),
+                       environment='$PY_ROOTDIR_PATH')
+
+    rootdir = testdir.mkdir("root")
+    rootdir.mkdir("tests")
+    testdir.makepyfile("""
+        import os
+        def test_one():
+            assert 1
+    """)
+
+    result = testdir.runpytest("--rootdir={}".format(path))
+    result.stdout.fnmatch_lines(['*rootdir: {}/root, inifile:*'.format(testdir.tmpdir), "*1 passed*"])
+
+
+def test_rootdir_wrong_option_arg(testdir):
+    testdir.makepyfile("""
+        import os
+        def test_one():
+            assert 1
+    """)
+
+    result = testdir.runpytest("--rootdir=wrong_dir")
+    result.stderr.fnmatch_lines(["*Directory *wrong_dir* not found. Check your '--rootdir' option.*"])