Algae exhibit the greatest variety of cell motility phenomena in the living world. These range from the peculiar gliding motility of filamentous blue green algae or cyanobacteria to chloroplast movements and cytoplasmic streaming which are most common in higher plants. In addition, cell motility by eukaryotic flagella is the characteristic mode of cell locomotion in algal flagellates and most reproductive cells of algae. Algae use these cell motility systems mainly to orient themselves or their photosynthetic organelles in a suitable light gradient to optimize growth and reproduction. In consequence most of the motility systems are coupled to photoreceptors and are regulated by signal transduction cascades. Algal cell motility has thus attracted consid erable interest also from non-phycologists and some algal motility systems have become models of research in cell and molecular biology. This book summarizes some of the progress that has been made in recent years in the analysis of cell motility phenomena in the algae. Although complete coverage of the subject was not attempted, the six chapters cover all the major types of cell motility systems and the authors provide in depth reviews of gliding motility, chloroplast movements, cytoplasmic streaming, flagellar beat pat terns, mechanisms of flagellar movement and centrin-mediated cell motility.