This book constitutes the refereed proceedings of the 27th International Symposium on Practical Aspects of Declarative Languages, PADL 2025, held in Denver, CO, USA, during January 20-21, 2025. The 15 full papers included in this book were carefully reviewed and selected from 26 submissions. The accepted papers span a range of topics related to functional and logic programming, including some novel applications of Answer Set Programming, language extensions, runtime monitoring, program transformations, type-checking, and applications of declarative programming techniques to artificial intelligence and machine learning, among others.