This volume documents the Phycomycetes, excluding Saprolegniaceae and Pythium, in both fresh and marine waters. It focuses on providing comprehensive descriptions while acknowledging inherent challenges in classifying organisms based on habitat. The preparation of this work was supported by various grants and contributions from colleagues, and it includes many original illustrations to supplement the text. The overarching goal is to present a cohesive account of these fascinating fungi, advancing our knowledge and understanding of their diverse and complex world.