diff --git a/pysnooper/tracer.py b/pysnooper/tracer.py
index 1b35154..e8eafc3 100644
--- a/pysnooper/tracer.py
+++ b/pysnooper/tracer.py
@@ -156,6 +156,14 @@ def get_write_function(output, overwrite):
     return write
 
 
+def _path_eq_or_sub(c, p):
+    # ref: https://stackoverflow.com/q/3812849/12388699
+    # assert file == os.path.realpath(file), 'property of frame.f_code.co_filename'
+    p_slash = os.path.join(p, '')
+    return c.rstrip(os.sep) == p.rstrip(os.sep) or \
+            os.path.commonprefix([c, p_slash]).rstrip(os.sep) == p.rstrip(os.sep)
+
+
 class FileWriter(object):
     def __init__(self, path, overwrite):
         self.path = pycompat.text_type(path)
@@ -200,6 +208,10 @@ class Tracer:
     Show snoop lines for functions that your function calls::
 
         @pysnooper.snoop(depth=2)
+    
+    Only snoop lines that are in the specified source directories::
+
+        @pysnooper.snoop(src_dir='path/to/myproj')
 
     Start all snoop lines with a prefix, to grep for them easily::
 
@@ -234,7 +246,7 @@ class Tracer:
     def __init__(self, output=None, watch=(), watch_explode=(), depth=1,
                  prefix='', overwrite=False, thread_info=False, custom_repr=(),
                  max_variable_length=100, normalize=False, relative_time=False,
-                 color=True):
+                 color=True, source_paths=[], exclude_paths=[]):
         self._write = get_write_function(output, overwrite)
 
         self.watch = [
@@ -264,7 +276,6 @@ class Tracer:
         self.relative_time = relative_time
         self.color = color and sys.platform in ('linux', 'linux2', 'cygwin',
                                                 'darwin')
-
         if self.color:
             self._FOREGROUND_BLUE = '\x1b[34m'
             self._FOREGROUND_CYAN = '\x1b[36m'
@@ -290,6 +301,18 @@ class Tracer:
             self._STYLE_NORMAL = ''
             self._STYLE_RESET_ALL = ''
 
+        def process_paths(paths):
+            ret = []
+            if isinstance(paths, str):
+                ret = [paths]
+            else:
+                assert isinstance(paths, list)
+                ret = paths
+            return list(map(os.path.realpath, ret))
+
+        self.source_paths = process_paths(source_paths)
+        self.exclude_paths = process_paths(exclude_paths)
+
     def __call__(self, function_or_class):
         if DISABLED:
             return function_or_class
@@ -406,6 +429,17 @@ class Tracer:
         # We should trace this line either if it's in the decorated function,
         # or the user asked to go a few levels deeper and we're within that
         # number of levels deeper.
+        if self.source_paths and not (
+            frame.f_code.co_filename[0] == '/' and # in case of '<frozen xxx>'
+            any(_path_eq_or_sub(frame.f_code.co_filename, p) for p in self.source_paths)
+        ):
+            return None
+        
+        if self.exclude_paths and (
+            frame.f_code.co_filename[0] == '/' and # in case of '<frozen xxx>'
+            any(_path_eq_or_sub(frame.f_code.co_filename, p) for p in self.exclude_paths)
+        ):
+            return None
 
         if not (frame.f_code in self.target_codes or frame in self.target_frames):
             if self.depth == 1: