diff --git a/usersimcrs/simulator/neural/core/transformer.py b/usersimcrs/simulator/neural/core/transformer.py
index 6727112b..4b91e354 100644
--- a/usersimcrs/simulator/neural/core/transformer.py
+++ b/usersimcrs/simulator/neural/core/transformer.py
@@ -1,4 +1,11 @@
-"""Encoder-only transformer model for neural user simulator."""
+"""Encoder-only transformer model for neural user simulator.
+
+Implementation inspired by PyTorch documentation and TUS's transformer model.
+
+Sources:
+https://colab.research.google.com/github/pytorch/tutorials/blob/gh-pages/_downloads/dca13261bbb4e9809d1a3aa521d22dd7/transformer_tutorial.ipynb#scrollTo=R8veciavth40
+https://gitlab.cs.uni-duesseldorf.de/general/dsml/tus_public/-/blob/master/convlab2/policy/tus/multiwoz/transformer.py?ref_type=heads
+"""
 
 import math
 
@@ -54,7 +61,6 @@ def __init__(
         nhead: int,
         hidden_dim: int,
         num_encoder_layers: int,
-        num_token: int,
         dropout: float = 0.5,
     ) -> None:
         """Initializes a encoder-only transformer model.
@@ -69,15 +75,15 @@ def __init__(
             dropout: Dropout rate. Defaults to 0.5.
         """
         super(TransformerEncoderModel, self).__init__()
-        self.d_model = input_dim
+        self.d_model = hidden_dim
 
-        self.pos_encoder = PositionalEncoding(input_dim, dropout)
-        self.embedding = nn.Embedding(num_token, input_dim)
+        self.pos_encoder = PositionalEncoding(hidden_dim, dropout)
+        self.embedding = nn.Linear(input_dim, hidden_dim)
 
         # Encoder layers
-        norm_layer = nn.LayerNorm(input_dim)
+        norm_layer = nn.LayerNorm(hidden_dim)
         encoder_layer = nn.TransformerEncoderLayer(
-            d_model=input_dim,
+            d_model=self.d_model,
             nhead=nhead,
             dim_feedforward=hidden_dim,
         )
@@ -87,7 +93,7 @@ def __init__(
             norm=norm_layer,
         )
 
-        self.linear = nn.Linear(input_dim, output_dim)
+        self.linear = nn.Linear(hidden_dim, output_dim)
         self.softmax = nn.Softmax(dim=-1)
 
         self.init_weights()
@@ -113,6 +119,8 @@ def forward(
         """
         src = self.embedding(src) * math.sqrt(self.d_model)
         src = self.pos_encoder(src)
-        output = self.encoder(src, mask=src_mask)
+        src = src.permute(1, 0, 2)
+        output = self.encoder(src, src_key_padding_mask=src_mask)
         output = self.linear(output)
+        output = output.permute(1, 0, 2)
         return output
diff --git a/usersimcrs/simulator/neural/tus/tus.py b/usersimcrs/simulator/neural/tus/tus.py
new file mode 100644
index 00000000..a668db5a
--- /dev/null
+++ b/usersimcrs/simulator/neural/tus/tus.py
@@ -0,0 +1,235 @@
+"""Transformer-based User Simulator (TUS)
+
+Reference: Domain-independent User Simulation with Transformers for
+Task-oriented Dialogue Systems, Lin et al., 2021.
+See: https://arxiv.org/abs/2106.08838
+
+Implementation is adapted from the description in the paper and the original
+implementation by the authors:
+https://gitlab.cs.uni-duesseldorf.de/general/dsml/tus_public
+"""
+
+import logging
+import random
+from collections import defaultdict
+from typing import Any, DefaultDict, Dict, List
+
+import torch
+
+from dialoguekit.core.dialogue_act import DialogueAct
+from dialoguekit.core.slot_value_annotation import SlotValueAnnotation
+from dialoguekit.core.utterance import Utterance
+from dialoguekit.nlg.nlg_conditional import ConditionalNLG
+from dialoguekit.nlu.nlu import NLU
+from dialoguekit.participant import DialogueParticipant
+from usersimcrs.core.simulation_domain import SimulationDomain
+from usersimcrs.dialogue_management.dialogue_state_tracker import (
+    DialogueStateTracker,
+)
+from usersimcrs.items.item_collection import ItemCollection
+from usersimcrs.simulator.neural.core.feature_handler import (
+    FeatureMask,
+    FeatureVector,
+)
+from usersimcrs.simulator.neural.core.transformer import (
+    TransformerEncoderModel,
+)
+from usersimcrs.simulator.neural.tus.tus_feature_handler import (
+    TUSFeatureHandler,
+)
+from usersimcrs.simulator.user_simulator import UserSimulator
+
+logger = logging.getLogger(__name__)
+
+
+class TUS(UserSimulator):
+    def __init__(
+        self,
+        id: str,
+        domain: SimulationDomain,
+        item_collection: ItemCollection,
+        nlu: NLU,
+        feature_handler: TUSFeatureHandler,
+        dialogue_state_tracker: DialogueStateTracker,
+        network_config: Dict[str, Any],
+        nlg: ConditionalNLG,
+    ) -> None:
+        """Initializes the Transformer-based User Simulator (TUS).
+
+        Args:
+            id: Simulator ID.
+            domain: Domain knowledge.
+            item_collection: Collection of items.
+            nlu: NLU module.
+            feature_handler: Feature handler.
+            dialogue_state_tracker: Dialogue state tracker.
+            network_config: Network configuration.
+            nlg: NLG module generating textual responses.
+        """
+        super().__init__(id=id, domain=domain, item_collection=item_collection)
+        self._nlu = nlu
+        self._nlg = nlg
+        self._tus_feature_handler = feature_handler
+        self._user_policy_network = TransformerEncoderModel(**network_config)
+        self._dialogue_state_tracker = dialogue_state_tracker
+        self._last_user_actions: DefaultDict[str, torch.Tensor] = defaultdict(
+            lambda: torch.tensor([])
+        )
+        self._last_turn_input: torch.Tensor = None
+
+    def initialize(self) -> None:
+        """Initializes the user simulator."""
+        self._dialogue_state_tracker.reset_state()
+        self._last_user_actions.clear()
+        self._last_turn_input = None
+
+    def _generate_response(self, agent_utterance: Utterance) -> Utterance:
+        """Generates response to the agent utterance.
+
+        Args:
+            agent_utterance: Agent utterance.
+
+        Returns:
+            User utterance.
+        """
+        previous_state = self._dialogue_state_tracker.get_current_state()
+        # 1. Perform NLU on the agent utterance, i.e., extract dialogue acts.
+        agent_dialogue_acts = self._nlu.extract_dialogue_acts(agent_utterance)
+
+        # 2. Update dialogue state based on the agent dialogue acts.
+        self._dialogue_state_tracker.update_state(
+            dialogue_acts=agent_dialogue_acts,
+            participant=DialogueParticipant.AGENT,
+        )
+
+        # 3. Extract features for the current turn.
+        turn_feature, mask = self._tus_feature_handler.build_input_vector(
+            agent_dialogue_acts=agent_dialogue_acts,
+            previous_state=previous_state,
+            state=self._dialogue_state_tracker.get_current_state(),
+            information_need=self.information_need,
+            user_action_vectors=self._last_user_actions,
+        )
+
+        # 5. Predict user dialogue acts based on the features.
+        user_dialogue_acts = self.predict_user_dialogue_acts(
+            turn_feature, mask, self._tus_feature_handler.action_slots
+        )
+
+        # 6. Generate user utterance based on the predicted dialogue acts.
+        response = self._nlg.generate_utterance_text(user_dialogue_acts)
+        response.participant = DialogueParticipant.USER
+
+        # 7. Update dialogue state based on the user dialogue acts.
+        self._dialogue_state_tracker.update_state(
+            dialogue_acts=response.dialogue_acts,
+            participant=DialogueParticipant.USER,
+        )
+
+        return response
+
+    def predict_user_dialogue_acts(
+        self,
+        features: List[FeatureVector],
+        mask: FeatureMask,
+        action_slots: List[str],
+    ) -> List[DialogueAct]:
+        """Predicts user dialogue acts based on the features.
+
+        Args:
+            features: Feature vector.
+            mask: Mask vector.
+            action_slots: Action slots used to predict the user action per slot.
+
+        Returns:
+            Predicted user dialogue acts.
+        """
+        output = self._user_policy_network(features, mask)
+        # fmt: off
+        output = output[
+            :, 1 : self._tus_feature_handler.max_turn_feature_length + 1, :  # noqa: E203, E501
+        ]
+        # fmt: on
+
+        slot_outputs: Dict[str, int] = {}
+        for index, slot_name in enumerate(action_slots):
+            o = int(torch.argmax(output[0, index + 1, :]).item())
+            assert o in range(6), f"Invalid output: {o}"
+            slot_outputs[slot_name] = o
+            # One-hot encoding of user action for the slot
+            o_i = torch.zeros(6)
+            o_i[o] = 1
+            self._last_user_actions[slot_name] = o_i
+
+        user_dialogue_acts = self._parse_policy_output(
+            action_slots, slot_outputs
+        )
+        return user_dialogue_acts
+
+    def _parse_policy_output(
+        self, action_slots: List[str], slot_outputs: Dict[str, int]
+    ) -> List[DialogueAct]:
+        """Parses the policy output to dialogue acts.
+
+        Args:
+            action_slots: Action slots.
+            slot_outputs: Output per slot.
+
+        Returns:
+            Dialogue acts.
+        """
+        belief_state = (
+            self._dialogue_state_tracker.get_current_state().belief_state
+        )
+        dialogue_acts = []
+
+        for slot in action_slots:
+            o = slot_outputs[slot]
+            dialogue_act = DialogueAct()
+
+            # Default intent is "inform"
+            dialogue_act.intent = "inform"
+
+            # Determine the value of the slot
+            if o == 1:
+                # The slot's value is requested by the user
+                dialogue_act.intent = "request"
+                dialogue_act.annotations.append(SlotValueAnnotation(slot))
+            elif o == 2:
+                # The slot's value is set to "dontcare"
+                dialogue_act.annotations.append(
+                    SlotValueAnnotation(slot, "dontcare")
+                )
+            elif o == 3:
+                # The slot's value is taken from the information need
+                if slot in self.information_need.constraints.keys():
+                    dialogue_act.annotations.append(
+                        SlotValueAnnotation(
+                            slot, self.information_need.constraints[slot]
+                        )
+                    )
+            elif o == 4:
+                # The slot's value was previously mentioned and is retrieved
+                # from the belief state
+                if slot in belief_state.keys():
+                    dialogue_act.annotations.append(
+                        SlotValueAnnotation(slot, belief_state[slot])
+                    )
+            elif o == 5:
+                # The slot's value in the information need is randomly modified
+                value = random.choice(
+                    list(
+                        self._item_collection.get_possible_property_values(slot)
+                    )
+                )
+                self.information_need.constraints[slot] = value
+                dialogue_act.annotations.append(
+                    SlotValueAnnotation(slot, value)
+                )
+            else:
+                logger.warning(f"{slot} is not mentioned in this turn.")
+                continue
+
+            dialogue_acts.append(dialogue_act)
+
+        return dialogue_acts
diff --git a/usersimcrs/simulator/neural/tus/tus_feature_handler.py b/usersimcrs/simulator/neural/tus/tus_feature_handler.py
index 1cab3dca..89fabc40 100644
--- a/usersimcrs/simulator/neural/tus/tus_feature_handler.py
+++ b/usersimcrs/simulator/neural/tus/tus_feature_handler.py
@@ -14,8 +14,8 @@
 import torch
 
 from dialoguekit.core.annotated_utterance import AnnotatedUtterance
-from dialoguekit.core.annotation import Annotation
 from dialoguekit.core.dialogue_act import DialogueAct
+from dialoguekit.core.slot_value_annotation import SlotValueAnnotation
 from usersimcrs.core.information_need import InformationNeed
 from usersimcrs.core.simulation_domain import SimulationDomain
 from usersimcrs.dialogue_management.dialogue_state import DialogueState
@@ -342,7 +342,7 @@ def build_input_vector(
         a special token. Note that is inferred from the list of feature vectors
         provided.
         The input vector is structured as follows:
-        [CLS] $V^t$ [SEP] $V^{t-1}$ [SEP] ... [SEP] $V^{t-n}$ [SEP] {padding},
+        [CLS] $V^t$ [SEP] $V^{t-1}$ [SEP] ... [SEP] $V^{t-n}$ [SEP] {padding}
         where {padding} indicates the padding to reach the maximum length.
 
         Args:
@@ -429,7 +429,7 @@ def get_label_vector(
 
     def _get_label(
         self,
-        annotation: Annotation,
+        slot_value_annotation: SlotValueAnnotation,
         current_state: DialogueState,
         information_need: InformationNeed,
     ) -> int:
@@ -445,42 +445,43 @@ def _get_label(
         5: The slot's value is randomly chosen.
 
         Args:
-            annotation: Annotation.
+            slot_value_annotation: Slot value pair annotation.
             current_state: Current state.
             information_need: Information need.
 
         Returns:
             Label.
         """
-        if annotation.value == "dontcare":
+        if slot_value_annotation.value == "dontcare":
             return 1
-        elif annotation.value is None:
+        elif slot_value_annotation.value is None:
             # The value is requested by the user
             return 2
-        elif annotation.value == information_need.get_constraint_value(
-            annotation.slot
-        ) or annotation.value == information_need.requested_slots.get(
-            annotation.slot
+        elif (
+            slot_value_annotation.value
+            == information_need.get_constraint_value(slot_value_annotation.slot)
+            or slot_value_annotation.value
+            == information_need.requested_slots.get(slot_value_annotation.slot)
         ):
             # The value is taken from the information need
             return 3
-        elif annotation.value == current_state.belief_state.get(
-            annotation.slot
+        elif slot_value_annotation.value == current_state.belief_state.get(
+            slot_value_annotation.slot
         ):
             # The value was previously mentioned and is
             # retrieved from the belief state
             return 4
         elif (
-            annotation.slot
+            slot_value_annotation.slot
             in [
                 information_need.constraints.keys(),
                 information_need.requested_slots.keys(),
                 current_state.belief_state.keys(),
             ]
-        ) and annotation.value not in [
-            information_need.get_constraint_value(annotation.slot),
-            information_need.requested_slots.get(annotation.slot),
-            current_state.belief_state.get(annotation.slot),
+        ) and slot_value_annotation.value not in [
+            information_need.get_constraint_value(slot_value_annotation.slot),
+            information_need.requested_slots.get(slot_value_annotation.slot),
+            current_state.belief_state.get(slot_value_annotation.slot),
         ]:
             # The slot's value is randomly chosen
             return 5
diff --git a/usersimcrs/simulator/user_simulator.py b/usersimcrs/simulator/user_simulator.py
index af238c4e..d8ef359d 100644
--- a/usersimcrs/simulator/user_simulator.py
+++ b/usersimcrs/simulator/user_simulator.py
@@ -17,7 +17,13 @@ def __init__(
         domain: SimulationDomain,
         item_collection: ItemCollection,
     ) -> None:
-        """Initializes the user simulator."""
+        """Initializes the user simulator.
+
+        Args:
+            id: User ID.
+            domain: Domain knowledge.
+            item_collection: Collection of items.
+        """
         super().__init__(id, UserType.SIMULATOR)
         self._domain = domain
         self._item_collection = item_collection