This guide discusses the integration of Generative AI (GenAI) and Large Language Models (LLMs) into eDiscovery workflows, particularly focusing on the ChatGPT model from OpenAI. It outlines the potential benefits of GenAI, including enhanced document review quality and efficiency, while reducing time and costs. The document explains the underlying technology of GenAI, detailing how advanced neural networks and transformers function to process and generate data. It also identifies key players in the GenAI space, such as OpenAI, Google, and Amazon, and notes their significant investments in this technology. Furthermore, the guide addresses important concepts like prompt engineering and grounding, which are essential for effective GenAI usage. Security and privacy concerns are also discussed, emphasizing the need for trusted providers and compliance with legal ethical requirements. Finally, the document presents various eDiscovery use cases for GenAI, including document summarization, relevancy assessment, and timeline creation, showcasing its versatility in legal contexts.