The rapid advancement of generative AI and specifically large language models (LLMs) is transforming the landscape of information systems (IS) engineering by offering unprecedented opportunities to support their design, development, maintenance, and reengineering. Starting with an overview of LLM history and foundational concepts, the book delves into practical applications for IS design and development, including prompt engineering, retrieval augmented generation, and multi-agent systems. Through a detailed survey and step-by-step programming guidance, readers will learn how to implement tools leveraging LLMs effectively. The book also addresses ethical considerations, offering insights and guidelines for responsible AI integration. The book provides a comprehensive and unified framework for exploiting LLMs in IS engineering. It aims at both researchers in information systems or LLM development and advanced professionals who would like to know how to potentially apply LLMs in the development or maintenance of information systems.