This chapter offers an overview of the evolution and significance of large language models (LLMs) in the field of artificial intelligence. It begins by tracing the historical development of language models, from early statistical approaches to modern neural and pre-trained models, culminating in the emergence of LLMs like GPT-3 and PaLM. The chapter then delves into the unique capabilities of LLMs, such as their ability to acquire vast world knowledge, solve complex tasks, and follow human instructions. It also highlights the key technological advancements that have driven their success, including scaling laws, data engineering, and large-scale pre-training. Furthermore, the chapter explores the challenges and opportunities presented by LLMs, particularly their potential to advance artificial intelligence and their transformative impact across various domains, including natural language processing, information retrieval, computer vision, and scientific research. Finally, the chapter concludes by outlining the structure and organization of this book, providing readers with a roadmap to navigate the subsequent discussions on LLM technology.