The present book is a monograph about a relatively large group of hypotrichous ciliates. It is the second of several volumes, which review the Hypotricha, one of the three major parts of the spirotrichs. The first volume treats the Oxytrichidae, also a large group, most species of which have 18 highly characteristically arranged frontal-ventr- transverse cirri and, more importantly, a comparatively complex dorsal ciliature due to fragmentation of dorsal kineties during cell division (Berger 1999). The present volume treats the Urostyloidea, which are characterised by a zigz- arrangement of the ventral cirri. Although this pattern is often very impressive, it is a rather simple feature originating by a more or less distinct increase of the number of frontal-ventral-transverse cirral anlagen to produce cirral pairs, which are serially - ranged in non-dividing specimens. Some users will be astonished that the monograph does not include Uroleptus, a group of tailed species, which also have a distinct zigz- ging cirral pattern. However, molecular and morphological data indicate that the zigzag pattern of Uroleptus evolved independently, that is, convergently to that of the uros- loids. Thus, it was excluded from the present review. Urostyloids are common in all major habitats, that is, freshwater, sea, and soil. The last detailed illustrated guide to this group of hypotrichs was provided by Kahl (1932).