This chapter explores the evolution and impact of Large Language Models (LLMs) and Generative Artificial Intelligence (GenAI). It traces the development from early Recurrent Neural Networks (RNNs) and Long Short-Term Memory (LSTM) networks to the Transformer architecture, which enabled parallel processing of text sequences and led to models like BERT and GPT. The chapter highlights key applications of LLMs, such as text summarization, translation, conversational AI, and creative content generation, illustrating how these models have revolutionized various industries. It also examines the ethical challenges posed by LLMs, including issues of bias, privacy concerns, and the spread of misinformation, emphasizing the need for responsible AI practices. The chapter concludes by looking ahead to future trends, such as multimodal models, few-shot learning, and efforts to improve energy efficiency, underscoring the pivotal role LLMs will play in shaping the future of AI.