diff --git a/batdetect2/targets/types.py b/batdetect2/targets/types.py
new file mode 100644
index 0000000..1a884bb
--- /dev/null
+++ b/batdetect2/targets/types.py
@@ -0,0 +1,132 @@
+"""Defines the core interface (Protocol) for the target definition pipeline.
+
+This module specifies the standard structure and methods expected from an object
+that encapsulates the configured logic for processing sound event annotations
+within the `batdetect2.targets` system.
+
+The main component defined here is the `TargetEncoder` protocol. This protocol
+acts as a contract, ensuring that components responsible for applying
+filtering, transformations, encoding annotations to class names, and decoding
+class names back to tags can be interacted with in a consistent manner
+throughout BatDetect2. It also defines essential metadata attributes expected
+from implementations.
+"""
+
+from typing import List, Optional, Protocol
+
+from soundevent import data
+
+__all__ = [
+    "TargetProtocol",
+]
+
+
+class TargetProtocol(Protocol):
+    """Protocol defining the interface for the target definition pipeline.
+
+    This protocol outlines the standard attributes and methods for an object
+    that encapsulates the complete, configured process for handling sound event
+    annotations to determine their target class for model training, and for
+    interpreting model predictions back into annotation tags.
+
+    Attributes
+    ----------
+    class_names : List[str]
+        An ordered list of the unique names of the specific target classes
+        defined by the configuration represented by this object.
+    generic_class_tags : List[data.Tag]
+        A list of `soundevent.data.Tag` objects representing the
+        generic class category (e.g., the default 'Bat' class tags used when
+        no specific class matches).
+    """
+
+    class_names: List[str]
+    """Ordered list of unique names for the specific target classes."""
+
+    generic_class_tags: List[data.Tag]
+    """List of tags representing the generic (unclassified) category."""
+
+    def filter(self, sound_event: data.SoundEventAnnotation) -> bool:
+        """Apply the filter to a sound event annotation.
+
+        Determines if the annotation should be included in further processing
+        and training based on the configured filtering rules.
+
+        Parameters
+        ----------
+        sound_event : data.SoundEventAnnotation
+            The annotation to filter.
+
+        Returns
+        -------
+        bool
+            True if the annotation should be kept (passes the filter),
+            False otherwise. Implementations should return True if no
+            filtering is configured.
+        """
+        ...
+
+    def transform(
+        self,
+        sound_event: data.SoundEventAnnotation,
+    ) -> data.SoundEventAnnotation:
+        """Apply tag transformations to an annotation.
+
+        Parameters
+        ----------
+        sound_event : data.SoundEventAnnotation
+            The annotation whose tags should be transformed.
+
+        Returns
+        -------
+        data.SoundEventAnnotation
+            A new annotation object with the transformed tags. Implementations
+            should return the original annotation object if no transformations
+            were configured.
+        """
+        ...
+
+    def encode(
+        self,
+        sound_event: data.SoundEventAnnotation,
+    ) -> Optional[str]:
+        """Encode a sound event annotation to its target class name.
+
+        Parameters
+        ----------
+        sound_event : data.SoundEventAnnotation
+            The (potentially filtered and transformed) annotation to encode.
+
+        Returns
+        -------
+        str or None
+            The string name of the matched target class if the annotation matches
+            a specific class definition. Returns None if the annotation does not
+            match any specific class rule (indicating it may belong to a generic
+            category or should be handled differently downstream).
+        """
+        ...
+
+    def decode(self, class_label: str) -> List[data.Tag]:
+        """Decode a predicted class name back into representative tags.
+
+        Parameters
+        ----------
+        class_label : str
+            The class name string (e.g., predicted by a model) to decode.
+
+        Returns
+        -------
+        List[data.Tag]
+            The list of tags corresponding to the input class name according
+            to the configuration. May return an empty list or raise an error
+            for unmapped labels, depending on the implementation's configuration
+            (e.g., `raise_on_unmapped` flag during building).
+
+        Raises
+        ------
+        ValueError, KeyError
+            Implementations might raise an error if the `class_label` is not
+            found in the configured mapping and error raising is enabled.
+        """
+        ...