diff --git a/chatmastermind/ais/openai.py b/chatmastermind/ais/openai.py
new file mode 100644
index 0000000..74438b8
--- /dev/null
+++ b/chatmastermind/ais/openai.py
@@ -0,0 +1,96 @@
+"""
+Implements the OpenAI client classes and functions.
+"""
+import openai
+from typing import Optional, Union
+from ..tags import Tag
+from ..message import Message, Answer
+from ..chat import Chat
+from ..ai import AI, AIResponse, Tokens
+from ..configuration import OpenAIConfig
+
+ChatType = list[dict[str, str]]
+
+
+class OpenAI(AI):
+    """
+    The OpenAI AI client.
+    """
+
+    def __init__(self, name: str, config: OpenAIConfig) -> None:
+        self.name = name
+        self.config = config
+
+    def request(self,
+                question: Message,
+                chat: Chat,
+                num_answers: int = 1,
+                otags: Optional[set[Tag]] = None) -> AIResponse:
+        """
+        Make an AI request, asking the given question with the given
+        chat history. The nr. of requested answers corresponds to the
+        nr. of messages in the 'AIResponse'.
+        """
+        # FIXME: use real 'system' message (store in OpenAIConfig)
+        oai_chat = self.openai_chat(chat, "system", question)
+        response = openai.ChatCompletion.create(
+            model=self.config.model,
+            messages=oai_chat,
+            temperature=self.config.temperature,
+            max_tokens=self.config.max_tokens,
+            top_p=self.config.top_p,
+            n=num_answers,
+            frequency_penalty=self.config.frequency_penalty,
+            presence_penalty=self.config.presence_penalty)
+        answers: list[Message] = []
+        for choice in response['choices']:  # type: ignore
+            answers.append(Message(question=question.question,
+                                   answer=Answer(choice['message']['content']),
+                                   tags=otags,
+                                   ai=self.name,
+                                   model=self.config.model))
+        return AIResponse(answers, Tokens(response['usage']['prompt'],
+                                          response['usage']['completion'],
+                                          response['usage']['total']))
+
+    def models(self) -> list[str]:
+        """
+        Return all models supported by this AI.
+        """
+        raise NotImplementedError
+
+    def print_models(self) -> None:
+        """
+        Print all models supported by the current AI.
+        """
+        not_ready = []
+        for engine in sorted(openai.Engine.list()['data'], key=lambda x: x['id']):
+            if engine['ready']:
+                print(engine['id'])
+            else:
+                not_ready.append(engine['id'])
+        if len(not_ready) > 0:
+            print('\nNot ready: ' + ', '.join(not_ready))
+
+    def openai_chat(self, chat: Chat, system: str,
+                    question: Optional[Message] = None) -> ChatType:
+        """
+        Create a chat history with system message in OpenAI format.
+        Optionally append a new question.
+        """
+        oai_chat: ChatType = []
+
+        def append(role: str, content: str) -> None:
+            oai_chat.append({'role': role, 'content': content.replace("''", "'")})
+
+        append('system', system)
+        for message in chat.messages:
+            if message.answer:
+                append('user', message.question)
+                append('assistant', message.answer)
+        if question:
+            append('user', question.question)
+        return oai_chat
+
+    def tokens(self, data: Union[Message, Chat]) -> int:
+        raise NotImplementedError