diff --git a/Makefile b/Makefile
index bb417b3..75a20bf 100644
--- a/Makefile
+++ b/Makefile
@@ -9,6 +9,7 @@ check:
 .PHONY: test
 test:
 	python tests/test_e2e.py
+	python tests/test_config.py
 
 .PHONY: fmt
 fmt:
diff --git a/devcluster/__init__.py b/devcluster/__init__.py
index f88653a..b47b656 100644
--- a/devcluster/__init__.py
+++ b/devcluster/__init__.py
@@ -18,6 +18,8 @@
     CustomConfig,
     CustomDockerConfig,
     AtomicConfig,
+    read_path,
+    deep_merge_configs,
 )
 from devcluster.recovery import ProcessTracker
 from devcluster.logger import Logger, Log, LogCB
diff --git a/devcluster/__main__.py b/devcluster/__main__.py
index 968e87e..5075a8c 100644
--- a/devcluster/__main__.py
+++ b/devcluster/__main__.py
@@ -2,18 +2,21 @@
 
 import argparse
 import contextlib
+import pathlib
 import fcntl
 import os
 import subprocess
 import re
 import sys
-from typing import Iterator, no_type_check, Optional, Sequence
+from typing import Iterator, List, no_type_check, Optional, Sequence
 
 import appdirs
 import yaml
 
 import devcluster as dc
 
+CONFIG_DIR = pathlib.Path(os.path.expanduser("~/.config/devcluster"))
+BASE_CONFIG_PATH = CONFIG_DIR / "_base.yaml"
 
 # prefer stdlib importlib.resources over pkg_resources, when available
 @no_type_check
@@ -52,7 +55,7 @@ def get_host_addr_for_docker() -> Optional[str]:
     if "darwin" in sys.platform:
         # On macOS, docker runs in a VM and host.docker.internal points to the IP
         # address of this VM.
-        return "host.docker.internal"
+        return os.getenv("DOCKER_LOCALHOST", "host.docker.internal")
 
     # On non-macOS, host.docker.internal does not exist. Instead, grab the source IP
     # address we would use if we had to talk to the internet. The sed command
@@ -98,7 +101,7 @@ def maybe_install_default_config() -> Optional[str]:
 
 def main() -> None:
     parser = argparse.ArgumentParser()
-    parser.add_argument("-c", "--config", dest="config", action="store")
+    parser.add_argument("-c", "--config", dest="config", action="store", nargs='+', help="Provide one or more config files")
     parser.add_argument("-1", "--oneshot", dest="oneshot", action="store_true")
     parser.add_argument("-q", "--quiet", dest="quiet", action="store_true")
     parser.add_argument("-C", "--cwd", dest="cwd", action="store")
@@ -114,6 +117,12 @@ def main() -> None:
     else:
         mode = "client"
 
+    blacklist = ["PGSERVICE"] # det binary lib/pq complains.
+    for key in blacklist:
+        if key in os.environ:
+            print(f"Unsetting {key} from environment")
+            del os.environ[key]
+
     # Validate args
     ok = True
     if mode == "client":
@@ -145,9 +154,30 @@ def main() -> None:
     if not ok:
         sys.exit(1)
 
+    def expand_path(path: str) -> pathlib.Path:
+        """
+        if the path doesn't exist try to match it with a known config name.
+        """
+        p = pathlib.Path(path)
+        # TODO: check if it looks like a config.
+        if not p.exists() or not p.is_file():
+            p = CONFIG_DIR / (path + ".yaml")
+            if not p.exists():
+                print(f"Path {path} does not exist", file=sys.stderr)
+                print("Available configs:")
+                for f in CONFIG_DIR.iterdir():
+                    if f.is_file():
+                        print(f"  {f.stem}")
+                sys.exit(1)
+            print(f"expaned {path} to {p}")
+        return p
+
+
     # Read config before the cwd.
+    config_paths: List[pathlib.Path] = []
     if args.config is not None:
-        config_path = args.config
+        for path in args.config:
+            config_paths.append(expand_path(path))
     else:
         check_paths = []
         # Always support ~/.devcluster.yaml
@@ -184,18 +214,29 @@ def main() -> None:
             sys.exit(1)
         env["DOCKER_LOCALHOST"] = docker_localhost
 
-    with open(config_path) as f:
-        config_body = yaml.safe_load(f.read())
-        if config_body is None:
-            print(f"config file '{config_path}' is an empty file!", file=sys.stderr)
-            sys.exit(1)
-        if not isinstance(config_body, dict):
-            print(
-                f"config file '{config_path}' does not represent a dict!",
-                file=sys.stderr,
-            )
-            sys.exit(1)
-        config = dc.Config(dc.expand_env(config_body, env))
+    def load_config_body(path: str) -> dict:
+        with open(path) as f:
+            config_body = yaml.safe_load(f.read())
+            if config_body is None:
+                print(f"config file '{path}' is an empty file!", file=sys.stderr)
+                sys.exit(1)
+            if not isinstance(config_body, dict):
+                print(
+                    f"config file '{path}' does not represent a dict!",
+                    file=sys.stderr,
+                )
+                sys.exit(1)
+        return config_body
+
+    config_bodies = [load_config_body(str(path)) for path in config_paths]
+    # base_config_body = load_config_body(str(BASE_CONFIG_PATH))
+    config = dc.Config(
+        *[
+            # dc.expand_env(conf_body, env) for conf_body in  [base_config_body] + config_bodies
+            dc.expand_env(conf_body, env) for conf_body in  config_bodies
+        ]
+    )
+
 
     # Process cwd.
     cwd_path = None
diff --git a/devcluster/config.py b/devcluster/config.py
index ee056c7..3a95d01 100644
--- a/devcluster/config.py
+++ b/devcluster/config.py
@@ -3,6 +3,8 @@
 import os
 import signal
 import string
+import typing
+import functools
 from typing import Any, Dict, List, Optional, Set
 
 import yaml
@@ -477,7 +479,7 @@ def __init__(self, config: Any) -> None:
         self.name = check_string(config["name"], "CustomConfig.name must be a string")
 
         self.env = config.get("env", {})
-        check_dict_with_string_keys(self.env, "CustomConfig.pre must be a list of dicts")
+        check_dict_with_string_keys(self.env, "CustomConfig.env must be dictionary")
 
         self.cwd = read_path(config.get("cwd"))
         if self.cwd is not None:
@@ -555,9 +557,59 @@ def read(config: Any) -> "CommandConfig":
             check_list_of_strings(config, msg)
         return CommandConfig(config)
 
+T = typing.TypeVar("T")
+def deep_merge(obj1: T, obj2: T, predicate) -> T:
+    if isinstance(obj1, dict) and isinstance(obj2, dict):
+        return deep_merge_dict(obj1, obj2, predicate)
+    elif isinstance(obj1, list) and isinstance(obj2, list):
+        return deep_merge_list(obj1, obj2, predicate)
+    else:
+        return obj2
+
+def deep_merge_dict(dict1, dict2, predicate):
+    result = dict1.copy()
+    for key, value in dict2.items():
+        if key in dict1:
+            result[key] = deep_merge(dict1[key], value, predicate)
+        else:
+            result[key] = value
+    return result
+
+def deep_merge_list(list1, list2, predicate):
+    result = list1.copy()
+    for item2 in list2:
+        if not any(predicate(item1, item2) for item1 in list1):
+            result.append(item2)
+        else:
+            for index, item1 in enumerate(list1):
+                if predicate(item1, item2):
+                    result[index] = deep_merge(item1, item2, predicate)
+    return result
+
+
+def deep_merge_configs(configs: typing.List[dict]) -> typing.Dict:
+    def should_merge(d1: dict, d2: dict) -> bool:
+        # is a stage
+        if d1.keys() == d2.keys() and len(d1.keys()) == 1:
+            return True
+
+        # is a rp
+        if d1.get("pool_name") is not None and d1.get("pool_name") == d2.get("pool_name"):
+            return True
+
+        return False
+
+    return functools.reduce(lambda x, y: deep_merge(x, y, should_merge), configs)
+
 
 class Config:
-    def __init__(self, config: Any) -> None:
+    def __init__(self, *configs: typing.Any) -> None:
+        assert len(configs) > 0, "must provide at least one config"
+        if len(configs) > 1:
+            config = deep_merge_configs(list(configs))
+        else:
+            config = configs[0]
+        assert isinstance(config, dict), "config must be a dict"
         allowed = {"stages", "commands", "startup_input", "temp_dir", "cwd"}
         required = {"stages"}
         check_keys(allowed, required, config, type(self).__name__)
@@ -575,3 +627,4 @@ def __init__(self, config: Any) -> None:
         self.cwd = read_path(config.get("cwd"))
         if self.cwd is not None:
             assert isinstance(self.cwd, str), "cwd must be a string"
+
diff --git a/tests/test_config.py b/tests/test_config.py
new file mode 100644
index 0000000..7fd6d36
--- /dev/null
+++ b/tests/test_config.py
@@ -0,0 +1,48 @@
+import devcluster as dc
+
+# test deep_merge_configs
+def test_deep_merge_configs():
+    # Test merge dicts
+    configs = [
+        {
+            "stages": [
+                {"stage1": {"param1": 1, "param2": 2}},
+                {"stage5": {"param2": 3, "param3": 4}},
+                {"stage4": {"param2": 3, "param3": 4}}
+            ]
+        },
+        {
+            "stages": [
+                {"stage1": {"param2": 3, "param3": 4}},
+                {"stage3": {"param2": 3, "param3": 4}}
+            ]
+        },
+    ]
+    merged = dc.deep_merge_configs(configs)
+    assert merged.get("stages")[0] == {"stage1": {"param1": 1, "param2": 3, "param3": 4}}
+
+    # Test merge lists of dicts with the same pool_name
+    configs = [
+        {"pools": [{"pool_name": "pool1", "param1": 1}, {"pool_name": "pool2", "param1": 1}]},
+        {"pools": [{"pool_name": "pool1", "param2": 2}, {"pool_name": "pool2", "param2": 2}]}
+    ]
+    merged = dc.deep_merge_configs(configs)
+    assert merged == {"pools": [
+        {"pool_name": "pool1", "param1": 1, "param2": 2},
+        {"pool_name": "pool2", "param1": 1, "param2": 2}
+    ]}
+
+    # Test merge lists of dicts with different pool_names
+    configs = [
+        {"pools": [{"pool_name": "pool1", "param1": 1}, {"pool_name": "pool2", "param1": 1}]},
+        {"pools": [{"pool_name": "pool3", "param1": 1}, {"pool_name": "pool4", "param1": 1}]}
+    ]
+    merged = dc.deep_merge_configs(configs)
+    assert merged == {"pools": [
+        {"pool_name": "pool1", "param1": 1},
+        {"pool_name": "pool2", "param1": 1},
+        {"pool_name": "pool3", "param1": 1},
+        {"pool_name": "pool4", "param1": 1}
+    ]}
+
+test_deep_merge_configs()