This book constitutes the thoroughly refereed post workshop proceedings of the 7th International Workshop on Approximation and Online Algorithms, WAOA 2009, held in Copenhagen, Denmark, in September 2009 as part of the ALGO 2009 conference event.The 22 revised full papers presented were carefully reviewed and selected from 62 submissions. The workshop covered areas such as algorithmic game theory, approximation classes, coloring and partitioning, competitive analysis, computational finance, cuts and connectivity, geometric problems, inapproximability results, mechanism design, network design, packing and covering, paradigms for design and analysis of approximation and online algorithms, parameterized complexity, randomization techniques, real-world applications, andscheduling problems.