diff --git a/fin_depo/data.py b/fin_depo/data.py
index 532bfbe..704ed55 100644
--- a/fin_depo/data.py
+++ b/fin_depo/data.py
@@ -109,25 +109,30 @@ class DepoFetcher(abc.ABC):
 
 @enforce_typing.enforce_types
 class DoubleRegister(abc.ABC):
+    """Information about some movement of assets."""
 
     @property
     @abc.abstractmethod
     def input(self) -> AssetAmount | None:
+        """How much and what kind of asset have been placed into the depository."""
         raise NotImplementedError
 
     @property
     @abc.abstractmethod
     def output(self) -> AssetAmount | None:
+        """How much and what kind of asset have been removed from the depository."""
         raise NotImplementedError
 
     @property
     @abc.abstractmethod
     def fee(self) -> AssetAmount | None:
+        """How much and what kind of asset was spent as a service fee."""
         raise NotImplementedError
 
     @property
     @abc.abstractmethod
     def executed_time(self) -> datetime.datetime:
+        """The precise point in time when the asset transaction was executed."""
         raise NotImplementedError
 
 
@@ -163,6 +168,15 @@ class TradeOrderDetails(DoubleRegister):
 @enforce_typing.enforce_types
 @dataclassabc.dataclassabc(frozen=True)
 class WithdrawalDetails(DoubleRegister):
+    """Information about a withdrawal of assets from a specific service.
+
+    Withdraw assets may appear in another depository as a `DepositDetails`, but
+    these cannot be automatically linked by `fin-depo`.
+
+    Includes both well-structured data about the order, and unstructured data
+    from the backend. The unstructured data might be needed for tax purposes.
+    """
+
     withdrawn: AssetAmount
     fee: AssetAmount
     executed_time: datetime.datetime
@@ -180,6 +194,15 @@ class WithdrawalDetails(DoubleRegister):
 @enforce_typing.enforce_types
 @dataclassabc.dataclassabc(frozen=True)
 class DepositDetails(DoubleRegister):
+    """Information about a deposit of assets to a specific service.
+
+    Deposited assets may appear in another depository as a `WithdrawalDetails`, but
+    these cannot be automatically linked by `fin-depo`.
+
+    Includes both well-structured data about the order, and unstructured data
+    from the backend. The unstructured data might be needed for tax purposes.
+    """
+
     deposit: AssetAmount
     fee: AssetAmount
     executed_time: datetime.datetime