diff --git a/outlines/index/index.py b/outlines/index/index.py
index 525c164b3..9c61bb84b 100644
--- a/outlines/index/index.py
+++ b/outlines/index/index.py
@@ -1,8 +1,14 @@
 from dataclasses import dataclass
-from typing import List, NewType, Optional, Protocol
+from typing import TYPE_CHECKING, List, NewType, Optional, Protocol
 
+import interegular
 import torch
 
+from outlines.index.fsm import create_fsm_index_tokenizer, make_deterministic_fsm
+
+if TYPE_CHECKING:
+    from outlines.models.tokenizer import Tokenizer
+
 FSMState = NewType("FSMState", int)
 
 
@@ -50,3 +56,46 @@ def is_final_state(self, state: FSMState) -> bool:
             return True
         else:
             return False
+
+
+class RegexFSM:
+    def __init__(
+        self,
+        regex_string: str,
+        tokenizer: "Tokenizer",
+        max_tokens: Optional[int] = None,
+    ):
+        regex_pattern = interegular.parse_pattern(regex_string)
+        regex_fsm, _ = make_deterministic_fsm(regex_pattern.to_fsm().reduce())
+        (
+            self.states_to_token_maps,
+            self.empty_token_ids,
+        ) = create_fsm_index_tokenizer(regex_fsm, tokenizer)
+
+        if not any(
+            regex_fsm.finals.intersection(v.values())
+            for v in self.states_to_token_maps.values()
+        ):
+            raise ValueError(
+                "The vocabulary does not allow us to build a sequence that matches the input regex"
+            )
+
+        self.max_tokens = max_tokens
+        self.num_tokens_generated = 0
+
+    def next_instructions(self, state: FSMState) -> GenerateInstruction:
+        return GenerateInstruction(list(self.states_to_token_maps[state].keys()))
+
+    def next_state(self, state: FSMState, token_id: torch.Tensor) -> FSMState:
+        self.num_tokens_generated += 1
+        last_token_to_end_state = self.states_to_token_maps[state]
+        return FSMState(last_token_to_end_state[token_id])
+
+    def is_final_state(self, state: FSMState) -> bool:
+        # Stop if the maximum number of tokens has been generated
+        # regardless of whether the stop token id has been found.
+        if self.max_tokens is not None:
+            if self.num_tokens_generated == self.max_tokens:
+                return True
+
+        return False