Large language models (LLMs) are reshaping customer experience (CX) in marketing by enabling interactions that are more adaptive, personalized, and contextually aware than any previous generation of AI. This entry provides a comprehensive review of how LLMs are transforming the design, delivery, and governance of CX across the customer journey. It begins by tracing the evolution of natural language processing, highlighting the architectural and conceptual advances that made today’s multimodal and agentic LLMs possible. The entry then examines six applied domains where LLMs are driving measurable impact: conversational customer support, hyper-personalized content creation, semantic search and discovery, compliance and policy communication, multilingual and culturally localized engagement, and emerging multimodal interfaces that integrate voice, vision, and real-time contextual feedback. Across these domains, the entry identifies both the transformative gains LLMs offer, such as speed, creative scale, intent recognition, and seamless multilingual interaction, and the critical risks they introduce, including hallucinations, regulatory exposure, privacy concerns, bias, and cultural misalignment. The entry concludes with an agenda for ethical and human-centered deployment, emphasizing governance, transparency, and hybrid human-AI collaboration. Overall, it positions LLMs as strategic, interactive touchpoints that increasingly define brand experience and customer relationships.