Social scientists have quickly adopted large language models (LLMs) for their ability to annotate documents without supervised training, an ability known as zero-shot classification. However, due to their computational demands, cost, and often proprietary nature, these models are frequently at odds with open science standards. This article introduces the Political Domain Enhanced BERT-based Algorithm for Textual Entailment (DEBATE) language models: Foundation models for zero-shot, few-shot, and supervised classification of political documents. As zero-shot classifiers, the models are designed to be used for common, well-defined tasks, such as topic and opinion classification. When used in this context, the DEBATE models are not only as good as state-of-the-art LLMs at zero-shot classification, but are orders of magnitude more efficient and completely open source. We further demonstrate that the models are effective few-shot learners. With a simple random sample of 10â25 documents, they can outperform supervised classifiers trained on hundreds or thousands of documents and state-of-the-art generative models. Additionally, we release the PolNLI dataset used to train these modelsâa corpus of over 200,000 political documents with highly accurate labels across over 800 classification tasks.