Soil fauna includes microscopic organisms such as nematodes (microfauna), mites and springtails (mesofauna), up to larger invertebrates such as worms, spiders, ants, termites and beetles (macrofauna) and vertebrates (megafauna) such as amphibians, reptiles and mammals. This chapter explains how their activity is important for soil health and can result in various ecosystem services, including provision of food and primary production, nutrient cycling and organic matter dynamics, water availability in soil, gas exchanges, soil formation, pollination and seed dispersal. The chapter classifies soil fauna and reviews currently available information on soil fauna biodiversity and functional roles worldwide, their role in soil health and the importance of management in determining soil fauna communities.