This book constitutes the thoroughly refereed post-proceedings of the 30th International Workshop on Graph-Theoretic Concepts in Computer Science, WG 2004, held in Bad Honnef, Germany in June 2004.The 31 revised full papers presented together with 2 invited papers were carefully selected from 66 submissions during two rounds of reviewing and improvement. The papers are organized in topical sections on graph algorithms: trees; graph algorithms: recognition and decomposition; graph algorithms: various problems; optimization and approximation algorithms; parameterized complexity and exponential algorithms; counting, combinatorics, and optimization; applications in bioinformatics and graph drawing; and graph classes and NP-hard problems.