This book constitutes the thoroughly refereed post-conference proceedings of the 4th Workshop on Combinatorial and Algorithmic Aspects of Networking, CAAN 2007, held in Halifax, Canada, in August 2007, co-located with the 10th Workshop on Algorithms and Data Structures, WADS 2007. The main focus is on strategies for searching in networks, and for cleaning networks of unwanted intruders, on different routing strategies, and on scheduling and load balancing.