Haskell is the world's leading lazy functional programming language and is widely used in teaching, research, and applications. The language continues to develop rapidly, but in 1998 the programming community decided to capture a stable snapshot of the language by introducing Haskell 98. This book constitutes the agreed definition of Haskell 98, the language itself as well as its supporting libraries, and should be a standard reference work for anyone involved in research, teaching, or applications. All Haskell compilers support Haskell 98, so professioanls and educators have a stable base for their work.