diff --git a/PFERD/downloaders.py b/PFERD/downloaders.py
index 0de6402..5d193f8 100644
--- a/PFERD/downloaders.py
+++ b/PFERD/downloaders.py
@@ -11,16 +11,16 @@ import requests.auth
 
 from .organizer import Organizer
 from .tmp_dir import TmpDir
+from .transform import Transformable
 from .utils import stream_to_path
 
 
 @dataclass
-class HttpDownloadInfo:
+class HttpDownloadInfo(Transformable):
     """
     This class describes a single file to be downloaded.
     """
 
-    path: Path
     url: str
     parameters: Dict[str, Any] = field(default_factory=dict)
 
diff --git a/PFERD/ilias/downloader.py b/PFERD/ilias/downloader.py
index e6bbf97..66243d1 100644
--- a/PFERD/ilias/downloader.py
+++ b/PFERD/ilias/downloader.py
@@ -10,6 +10,7 @@ import requests
 
 from ..organizer import Organizer
 from ..tmp_dir import TmpDir
+from ..transform import Transformable
 from ..utils import soupify, stream_to_path
 from .authenticators import IliasAuthenticator
 
@@ -19,12 +20,11 @@ class ContentTypeException(Exception):
 
 
 @dataclass
-class IliasDownloadInfo:
+class IliasDownloadInfo(Transformable):
     """
     This class describes a single file to be downloaded.
     """
 
-    path: Path
     url: str
     modification_date: datetime.datetime
     # parameters: Dict[str, Any] = field(default_factory=dict)
diff --git a/PFERD/transform.py b/PFERD/transform.py
new file mode 100644
index 0000000..5427464
--- /dev/null
+++ b/PFERD/transform.py
@@ -0,0 +1,42 @@
+"""
+Transforms let the user define functions to decide where the downloaded files
+should be placed locally. They let the user do more advanced things like moving
+only files whose names match a regex, or renaming files from one numbering
+scheme to another.
+"""
+
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Callable, List, Optional, TypeVar
+
+
+Transform = Callable[[Path], Optional[Path]]
+
+
+@dataclass
+class Transformable:
+    """
+    An object that can be transformed by a Transform.
+    """
+
+    path: Path
+
+
+TF = TypeVar("TF", bound=Transformable)
+
+
+def apply_transform(
+        transform: Callable[[Path], Optional[Path]],
+        transformables: List[TF],
+) -> List[TF]:
+    """
+    Apply a Transform to multiple Transformables, discarding those that were
+    not transformed by the Transform.
+    """
+
+    result: List[TF] = []
+    for transformable in transformables:
+        if new_path := transform(transformable.path):
+            transformable.path = new_path
+            result.append(transformable)
+    return result