diff --git a/muxplex/service.py b/muxplex/service.py
new file mode 100644
index 0000000..1412374
--- /dev/null
+++ b/muxplex/service.py
@@ -0,0 +1,164 @@
+"""muxplex/service.py — System service management (systemd on Linux, launchd on macOS)."""
+
+import shutil
+import sys
+from pathlib import Path
+
+# ---------------------------------------------------------------------------
+# Constants
+# ---------------------------------------------------------------------------
+
+_SYSTEMD_UNIT_DIR: Path = Path.home() / ".config" / "systemd" / "user"
+_SYSTEMD_UNIT_PATH: Path = _SYSTEMD_UNIT_DIR / "muxplex.service"
+
+_LAUNCHD_PLIST_DIR: Path = Path.home() / "Library" / "LaunchAgents"
+_LAUNCHD_PLIST_PATH: Path = _LAUNCHD_PLIST_DIR / "com.muxplex.plist"
+_LAUNCHD_LABEL: str = "com.muxplex"
+
+# ---------------------------------------------------------------------------
+# Platform detection
+# ---------------------------------------------------------------------------
+
+
+def _is_darwin() -> bool:
+    """Return True if running on macOS."""
+    return sys.platform == "darwin"
+
+
+def _resolve_muxplex_bin() -> str:
+    """Return the muxplex binary path.
+
+    Prefers the ``muxplex`` executable on PATH; falls back to
+    ``<sys.executable> -m muxplex`` when not found.
+    """
+    which = shutil.which("muxplex")
+    if which:
+        return which
+    return f"{sys.executable} -m muxplex"
+
+
+# ---------------------------------------------------------------------------
+# Private stubs — systemd (Linux)
+# ---------------------------------------------------------------------------
+
+
+def _systemd_install() -> None:
+    raise NotImplementedError("systemd install not implemented")
+
+
+def _systemd_uninstall() -> None:
+    raise NotImplementedError("systemd uninstall not implemented")
+
+
+def _systemd_start() -> None:
+    raise NotImplementedError("systemd start not implemented")
+
+
+def _systemd_stop() -> None:
+    raise NotImplementedError("systemd stop not implemented")
+
+
+def _systemd_restart() -> None:
+    raise NotImplementedError("systemd restart not implemented")
+
+
+def _systemd_status() -> None:
+    raise NotImplementedError("systemd status not implemented")
+
+
+def _systemd_logs() -> None:
+    raise NotImplementedError("systemd logs not implemented")
+
+
+# ---------------------------------------------------------------------------
+# Private stubs — launchd (macOS)
+# ---------------------------------------------------------------------------
+
+
+def _launchd_install() -> None:
+    raise NotImplementedError("launchd install not implemented")
+
+
+def _launchd_uninstall() -> None:
+    raise NotImplementedError("launchd uninstall not implemented")
+
+
+def _launchd_start() -> None:
+    raise NotImplementedError("launchd start not implemented")
+
+
+def _launchd_stop() -> None:
+    raise NotImplementedError("launchd stop not implemented")
+
+
+def _launchd_restart() -> None:
+    raise NotImplementedError("launchd restart not implemented")
+
+
+def _launchd_status() -> None:
+    raise NotImplementedError("launchd status not implemented")
+
+
+def _launchd_logs() -> None:
+    raise NotImplementedError("launchd logs not implemented")
+
+
+# ---------------------------------------------------------------------------
+# Public API — platform-dispatching wrappers
+# ---------------------------------------------------------------------------
+
+
+def service_install() -> None:
+    """Install the muxplex service unit for the current user."""
+    if _is_darwin():
+        _launchd_install()
+    else:
+        _systemd_install()
+
+
+def service_uninstall() -> None:
+    """Remove the muxplex service unit for the current user."""
+    if _is_darwin():
+        _launchd_uninstall()
+    else:
+        _systemd_uninstall()
+
+
+def service_start() -> None:
+    """Start the muxplex service."""
+    if _is_darwin():
+        _launchd_start()
+    else:
+        _systemd_start()
+
+
+def service_stop() -> None:
+    """Stop the muxplex service."""
+    if _is_darwin():
+        _launchd_stop()
+    else:
+        _systemd_stop()
+
+
+def service_restart() -> None:
+    """Restart the muxplex service."""
+    if _is_darwin():
+        _launchd_restart()
+    else:
+        _systemd_restart()
+
+
+def service_status() -> None:
+    """Print the current status of the muxplex service."""
+    if _is_darwin():
+        _launchd_status()
+    else:
+        _systemd_status()
+
+
+def service_logs() -> None:
+    """Stream or print logs for the muxplex service."""
+    if _is_darwin():
+        _launchd_logs()
+    else:
+        _systemd_logs()
diff --git a/muxplex/tests/test_service.py b/muxplex/tests/test_service.py
new file mode 100644
index 0000000..05d8afe
--- /dev/null
+++ b/muxplex/tests/test_service.py
@@ -0,0 +1,36 @@
+"""Tests for muxplex/service.py — system service management module."""
+
+import sys
+
+
+def test_service_module_importable():
+    """All 7 public service functions must be importable from muxplex.service."""
+    from muxplex.service import (  # noqa: F401
+        service_install,
+        service_logs,
+        service_restart,
+        service_start,
+        service_status,
+        service_stop,
+        service_uninstall,
+    )
+
+
+def test_is_darwin_detection(monkeypatch):
+    """_is_darwin() must return True when sys.platform=='darwin', False for 'linux'."""
+    from muxplex.service import _is_darwin
+
+    monkeypatch.setattr(sys, "platform", "darwin")
+    assert _is_darwin() is True
+
+    monkeypatch.setattr(sys, "platform", "linux")
+    assert _is_darwin() is False
+
+
+def test_resolve_muxplex_bin():
+    """_resolve_muxplex_bin() must return a string containing 'muxplex' or 'python'."""
+    from muxplex.service import _resolve_muxplex_bin
+
+    result = _resolve_muxplex_bin()
+    assert isinstance(result, str)
+    assert "muxplex" in result or "python" in result