Protozoa are active components of the soil microfauna. For example, they may stimulate bacterial metabolism and some fungal metabolites can lyse protozoa. They may be predators of bacteria and hence have a role in biological control. Their presence in groundwaters can be used as an indicator of pollution, while they are also being used to treat sewage in the activated-sludge and reed-bed processes. They are believed to be major secondary decomposers in soil and increased knowledge about these microorganisms is important to sustain soil fertility and food production. This book is the first in English for 65 years devoted entirely to soil protozoology. It is written by experienced microbiologists and should be of interest to protozoologists, other microbiologists, and soil scientists.