This chapter establishes the conceptual foundations of human–AI communication by clarifying what it means to communicate with generative AI systems and how this differs fundamentally from traditional models of human–computer interaction. It introduces communication with AI as an interpretive, context-dependent and collaborative process rather than a sequence of commands or instructions. The chapter examines how generative models interpret human input, why users require accurate mental models of AI behaviour and how context, memory and multimodality shape interaction outcomes. By integrating perspectives from human–computer interaction, communication theory and cognitive psychology, the chapter provides a coherent framework for understanding AI communication as a distinct and emerging human competence. This foundation prepares the reader for the principles, techniques and practices of effective communication with generative AI developed in subsequent chapters.