ell is a lightweight programming library for language models that treats prompts as functions rather than mere strings. The design of ell is based on years of experience building and utilizing language models within OpenAI and the startup ecosystem. It provides a novel programming approach, allowing developers to generate string prompts or message lists sent to the language model by defining functions. This encapsulation creates a clear interface for users, allowing them to focus solely on the data required by the LMP. ell also offers a wealth of tools supporting monitoring, version control, and visualization, transforming prompt engineering from an obscure art into a precise science.