This entry introduces the application programming interface (API) and its pivotal role in integrating generative AI, such as ChatGPT, into language learning within the computer-assisted language learning (CALL) framework. It begins by explaining the concept of APIs and detailing the process for obtaining API keys. The entry then showcases practical examples of how the OpenAI API can be employed in desktop applications and Python programming to enhance data-driven learning (DDL) and automate tasks like automated essay scoring. It also delves into crucial considerations for using APIs, including cost implications, the selection of suitable model versions, and the necessity of sharing code and parameters to guarantee research reproducibility. Furthermore, the entry discusses ethical considerations essential for responsible AI utilization. Concluding with a discussion on the transformative potential of APIs, the entry encourages readers to explore and experiment with this technology, thereby gaining a foundational understanding that can leverage digital advancements in language education.