This special double issue of Mathematical Structures in Computer Science is in honour of Roger Hindley and is devoted to the topic of lambda-calculus and logic.

It is a great pleasure for us to greet Roger Hindley on the occasion of his retirement from the University of Wales, Swansea, and his 60th birthday. We have known Roger for many years and we have had the chance to collaborate with him and appreciate his intellectual standard, his remarkable mathematical rigor, and his inexhaustible sense of humour. This has enabled Roger to step back critically even in the face of a difficult mathematical task and help to solve it by a new way of looking at it.

Roger Hindley's dissertation concerned the Church–Rosser Theorem and was a significant contribution to the topic. His subsequent work spanned many aspects of lambda-calculus, covering both its models and applications. To mention just a few, he produced work on axioms for Curry's strong (eta) reduction, comparing lambda and combinatory reductions (and models), models for type assignment, and formulas as types for some nonstandard systems (intersection types, BCK systems, etc.).

Roger Hindley collaborated with Jonathan Seldin on two well-known introductory books on the subject (Bruce Lercher also collaborated as an author on the first of these). More recently, he has published an introduction to type assignment. He was also co-author with H. B. Curry and J. Seldin on Combinatory Logic, vol. II, which is an important research publication on the subject.

Roger has played an important role in the lambda-calculus community over the years as that community has grown; in particular, he has been an active organiser of many conferences on the topic. In fact, his success in disseminating knowledge about the lambda calculus, particularly in the United Kingdom, means that Roger may be considered a ‘Godfather’ of ML and its type system.

(In preparing this special issue of Mathematical Structures in Computer Science, we have been fortunate enough to receive too many excellent papers for one double issue. As a result, additional papers by colleagues who wish to honour Roger will appear in future issues of this journal.)