This book contains invited and contributed papers on combinatorics, random graphs and networks, algorithms analysis and trees, branching processes, constituting the Proceedings of the 3rd International Colloquium on Mathematics and Computer Science that will be held in Vienna in September 2004. It addresses a large public in applied mathematics, discrete mathematics and computer science, including researchers, teachers, graduate students and engineers. They will find here current questions in Computer Science and the related modern and powerful mathematical methods. The range of applications is very wide and goes beyond Computer Science.