The book "User-Centric Ultra-Dense Networks for 5G" provides a comprehensive introduction to the concept of user-centric ultra-dense networks (UUDN) for 5G technology. It addresses the challenges, architecture, and key technologies associated with this new network architecture. The authors propose an innovative model based on the decoupling of user and control functions, optimizing the interaction between users and the network. The four main features of UUDN are explained in detail, focusing on intelligent, dynamic, and secure networks that adapt to users' needs. Additionally, promising technological directions such as dynamic access point grouping and advanced interference management are discussed. The book is aimed at both beginners looking to familiarize themselves with the topic and professionals interested in the advancement and standardization in this field.