This review examines the following questions: (1) do soil fauna play an important regulatory role in decomposition and mineralization processes in arid and semiarid ecosystems? (2) if important, what are the mechanisms of the rate regulation, and (3) what are the management implications of these relationships? Because termites process more than half of the surface litter in hot deserts, this review focuses on faunal effects on buried litter and roots. Elimination of soil arthropods reduced rates of mass loss and coupled mass loss to soil moisture. With arthropods present soil moisture accounted for less than 50% of the variation in mass loss. Other experiments demonstrated that regulation of mass loss results from predatory mites regulating the population density of grazers, thereby preventing overgrazing of the fungi and bacteria. The regulation of microbial grazers by soil microarthropods also affects rates of mineralization and nutrient immobilization. Populations of small fungus grazing mites (Tarsonomidae) affect mineralization directly. Microarthropods tend to uncouple mineralization from abiotic constraints. Fluctuations in microbial populations and soil fauna are more a function of substrate availability than of abiotic regulation. Pulses in organic matter inputs result in periods of nutrient immobilization, the extent of which is a function of the rate of recovery of populations of key soil microarthropods.