diff --git a/sentry_sdk/client.py b/sentry_sdk/client.py
index 168198adb9..bc9048214b 100644
--- a/sentry_sdk/client.py
+++ b/sentry_sdk/client.py
@@ -12,6 +12,8 @@
     disable_capture_event,
     format_timestamp,
     get_type_name,
+    get_default_release,
+    get_default_environment,
     handle_in_app,
     logger,
 )
@@ -62,10 +64,10 @@ def _get_options(*args, **kwargs):
         rv["dsn"] = os.environ.get("SENTRY_DSN")
 
     if rv["release"] is None:
-        rv["release"] = os.environ.get("SENTRY_RELEASE")
+        rv["release"] = get_default_release()
 
     if rv["environment"] is None:
-        rv["environment"] = os.environ.get("SENTRY_ENVIRONMENT")
+        rv["environment"] = get_default_environment(rv["release"])
 
     if rv["server_name"] is None and hasattr(socket, "gethostname"):
         rv["server_name"] = socket.gethostname()
diff --git a/sentry_sdk/utils.py b/sentry_sdk/utils.py
index 2a8798adb0..d39b0c1e40 100644
--- a/sentry_sdk/utils.py
+++ b/sentry_sdk/utils.py
@@ -4,6 +4,7 @@
 import os
 import sys
 import threading
+import subprocess
 
 from datetime import datetime
 
@@ -52,6 +53,57 @@ def _get_debug_hub():
     pass
 
 
+def get_default_release():
+    # type: () -> Optional[str]
+    """Try to guess a default release."""
+    release = os.environ.get("SENTRY_RELEASE")
+    if release:
+        return release
+
+    with open(os.path.devnull, "w+") as null:
+        try:
+            release = (
+                subprocess.Popen(
+                    ["git", "rev-parse", "--short", "HEAD"],
+                    stdout=subprocess.PIPE,
+                    stderr=null,
+                    stdin=null,
+                )
+                .communicate()[0]
+                .strip()
+                .decode("utf-8")
+            )
+        except (OSError, IOError):
+            pass
+
+        if release:
+            return release
+
+    for var in (
+        "HEROKU_SLUG_COMMIT",
+        "SOURCE_VERSION",
+        "CODEBUILD_RESOLVED_SOURCE_VERSION",
+        "CIRCLE_SHA1",
+        "GAE_DEPLOYMENT_ID",
+    ):
+        release = os.environ.get(var)
+        if release:
+            return release
+    return None
+
+
+def get_default_environment(
+    release=None,  # type: Optional[str]
+):
+    # type: (...) -> Optional[str]
+    rv = os.environ.get("SENTRY_ENVIRONMENT")
+    if rv:
+        return rv
+    if release is not None:
+        return "production"
+    return None
+
+
 class CaptureInternalException(object):
     __slots__ = ()