Discovered over a century ago, the centrosome is the major microtubule organizing center of the animal cell. It is a tiny organelle of surprising structural complexity. Over the last few years our understanding of the structure and composition of centrosomes has greatly advanced, and the demonstration of frequent centrosome anomalies in most common human tumors has sparked additional interest in the role of this organelle in a broader scientific community.The centrosome controls the number and distribution of microtubulesa major element of the cell cytoskeletonand hence influences many important cellular functions and properties. These include cell shape, polarity, and motility, as well as the intracellular transport and positioning of various organelles. Of particular interest, centrosome function is critical for chromosome segregation and cell division.This book is meant to summarize our current knowledge of the structure, function and evolution of microtubule organizing centers, primarily centrosomes. Emphasis is on the role of these organelles in development and disease (particularly cancer).