Reactions on Monadic Lenses -- Conation Confers Concurrency -- Counting Successes: Effects and Transformations for Non-deterministic Programs -- The Essence of Inheritance -- Subtyping Supports Safe Session Substitution -- Proof Relevant Parametricity -- Comprehending Ringads -- Dragging Proofs out of Pictures -- Experiences with QuickCheck: Testing the Hard Stuff and Staying Sane -- Cutting out Continuations -- The Lambda Calculus: Practice and Principle -- I Got Plenty o' Nuttin' -- Pointlessness Is Better than Listlessness -- The Essence of Dependent Object Types -- Linear lambda-mu Is CP (more or less) -- A Reaction on types -- The Essence of Multi-Stage Evaluation in LMS -- 1ML with Special Effects -- The Computer Scientist Nightmare -- A Branding Strategy for Business Types -- The Recursive Union of Some Gradual Types -- A Delta for Hybrid Type Checking -- Certifying Data in Multiparty Session Types -- Recursion Equations as a Programming Language. .

This volume is published in Honor of Philip Wadler on the occasion of his 60th birthday, and the collection of papers form a Festschrift for him. The contributions are made by some of the many who know Phil and have been influenced by him. The research papers included here represent some of the areas in which Phil has been active, and the editors thank their colleagues for agreeing to contribute to this Festschrift. We attempt to summarize Phil Wadler's scientific achievements. In addition, we describe the personal style and enthusiasm that Phil has brought to the subject.