This book constitutes the refereed proceedings of the First International Conference on Algebra and Coalgebra in Computer Science, CALCO 2005, held in Swansea, UK in September 2005. The biennial conference was created by joining the International Workshop on Coalgebraic Methods in Computer Science (CMCS) and the Workshop on Algebraic Development Techniques (WADT). It addresses two basic areas of application for algebras and coalgebras - as mathematical objects as well as their application in computer science.

The 25 revised full papers presented together with 3 invited papers were...