diff --git a/pyproject.toml b/pyproject.toml
index fe7ecdba..898eae5a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -17,6 +17,7 @@ dependencies = [
     "uvicorn",
     "sqlalchemy",
     "mysqlclient",
+    "python_dotenv",
 ]
 
 [project.optional-dependencies]
diff --git a/src/config.py b/src/config.py
new file mode 100644
index 00000000..ae425f96
--- /dev/null
+++ b/src/config.py
@@ -0,0 +1,45 @@
+import functools
+import os
+import tomllib
+import typing
+from pathlib import Path
+
+from dotenv import load_dotenv
+
+TomlTable = dict[str, typing.Any]
+
+
+def _apply_defaults_to_siblings(configuration: TomlTable) -> TomlTable:
+    defaults = configuration["defaults"]
+    return {
+        subtable: (defaults | overrides) if isinstance(overrides, dict) else overrides
+        for subtable, overrides in configuration.items()
+        if subtable != "defaults"
+    }
+
+
+@functools.cache
+def load_database_configuration(file: Path = Path(__file__).parent / "config.toml") -> TomlTable:
+    configuration = tomllib.loads(file.read_text())
+
+    database_configuration = _apply_defaults_to_siblings(
+        configuration["databases"],
+    )
+    load_dotenv()
+    database_configuration["openml"]["username"] = os.environ.get(
+        "OPENML_DATABASES_OPENML_USERNAME",
+        "root",
+    )
+    database_configuration["openml"]["password"] = os.environ.get(
+        "OPENML_DATABASES_OPENML_PASSWORD",
+        "ok",
+    )
+    database_configuration["expdb"]["username"] = os.environ.get(
+        "OPENML_DATABASES_EXPDB_USERNAME",
+        "root",
+    )
+    database_configuration["expdb"]["password"] = os.environ.get(
+        "OPENML_DATABASES_EXPDB_PASSWORD",
+        "ok",
+    )
+    return database_configuration
diff --git a/src/config.toml b/src/config.toml
new file mode 100644
index 00000000..f85d9a06
--- /dev/null
+++ b/src/config.toml
@@ -0,0 +1,11 @@
+[databases.defaults]
+host="127.0.0.1"
+port="3306"
+# SQLAlchemy `dialect` and `driver`: https://docs.sqlalchemy.org/en/20/dialects/index.html
+drivername="mysql"
+
+[databases.expdb]
+database="openml_expdb"
+
+[databases.openml]
+database="openml"
diff --git a/src/database/datasets.py b/src/database/datasets.py
index f794aeae..1e534396 100644
--- a/src/database/datasets.py
+++ b/src/database/datasets.py
@@ -1,17 +1,22 @@
 """ Translation from https://github.com/openml/OpenML/blob/c19c9b99568c0fabb001e639ff6724b9a754bbc9/openml_OS/models/api/v1/Api_data.php#L707"""
 from typing import Any
 
+from config import load_database_configuration
 from sqlalchemy import create_engine, text
+from sqlalchemy.engine import URL
 
 from database.meta import get_column_names
 
+_database_configuration = load_database_configuration()
+expdb_url = URL.create(**_database_configuration["expdb"])
 expdb = create_engine(
-    "mysql://root:ok@127.0.0.1:3306/openml_expdb",
+    expdb_url,
     echo=True,
     pool_recycle=3600,
 )
+openml_url = URL.create(**_database_configuration["openml"])
 openml = create_engine(
-    "mysql://root:ok@127.0.0.1:3306/openml",
+    openml_url,
     echo=True,
     pool_recycle=3600,
 )
diff --git a/tests/config_test.py b/tests/config_test.py
new file mode 100644
index 00000000..412606d1
--- /dev/null
+++ b/tests/config_test.py
@@ -0,0 +1,35 @@
+import os
+from pathlib import Path
+
+from config import _apply_defaults_to_siblings, load_database_configuration
+
+
+def test_apply_defaults_to_siblings_applies_defaults() -> None:
+    input_ = {"defaults": {1: 1}, "other": {}}
+    expected = {"other": {1: 1}}
+    output = _apply_defaults_to_siblings(input_)
+    assert expected == output
+
+
+def test_apply_defaults_to_siblings_does_not_override() -> None:
+    input_ = {"defaults": {1: 1}, "other": {1: 2}}
+    expected = {"other": {1: 2}}
+    output = _apply_defaults_to_siblings(input_)
+    assert expected == output
+
+
+def test_apply_defaults_to_siblings_ignores_nontables() -> None:
+    input_ = {"defaults": {1: 1}, "other": {1: 2}, "not-a-table": 3}
+    expected = {"other": {1: 2}, "not-a-table": 3}
+    output = _apply_defaults_to_siblings(input_)
+    assert expected == output
+
+
+def test_load_configuration_adds_environment_variables(default_configuration_file: Path) -> None:
+    database_configuration = load_database_configuration(default_configuration_file)
+    assert database_configuration["openml"]["username"] == "root"
+
+    load_database_configuration.cache_clear()
+    os.environ["OPENML_DATABASES_OPENML_USERNAME"] = "foo"
+    database_configuration = load_database_configuration(default_configuration_file)
+    assert database_configuration["openml"]["username"] == "foo"
diff --git a/tests/conftest.py b/tests/conftest.py
index fead0652..45c68f1e 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,20 +1,27 @@
 import json
-import pathlib
+from pathlib import Path
 from typing import Any, Generator
 
 import pytest
 from fastapi import FastAPI
 from fastapi.testclient import TestClient
-from main import app
 
 
 @pytest.fixture()
 def api_client() -> Generator[FastAPI, None, None]:
+    # We want to avoid starting a test client app if tests don't need it.
+    from main import app
+
     return TestClient(app)
 
 
 @pytest.fixture()
 def dataset_130() -> Generator[dict[str, Any], None, None]:
-    json_path = pathlib.Path(__file__).parent / "resources" / "datasets" / "dataset_130.json"
+    json_path = Path(__file__).parent / "resources" / "datasets" / "dataset_130.json"
     with json_path.open("r") as dataset_file:
         yield json.load(dataset_file)
+
+
+@pytest.fixture()
+def default_configuration_file() -> Path:
+    return Path().parent.parent / "src" / "config.toml"