This book constitutes the refereed proceedings of the18th International Symposium on Practical Aspects of Declarative Languages,PADL 2016, held in St. Petersburg, FL, USA, in January 2016.The 11 revised papers presented were carefully reviewedand selected from 17 initial submissions for inclusion in the book. PADL is a forumfor researchers and practitioners to present original work emphasizing novelapplications and implementation techniques for all forms of declarativeconcepts, including, functional, logic, constraints, etc.