This book constitutes the refereed proceedings of the Third International Workshop on Parameterized and Exact Computation, IWPEC 2008, held in Victoria, Canada, in May 2008 - co-located with the 40th ACM Symposium on Theory of Computing, STOC 2008. The 17 revised full papers presented together with 3 invited lectures were carefully reviewed and selected from 32 submissions. The topics addressed cover research in all aspects of parameterized and exact...