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.