The occurrence and ecological importance of vesicular-arbuscular mycorrhizal (VAM) fungi have been extensively studied in certain plant communities such as the tropical rain forest and sand dunes, but much less extensive information is available on the ecology of the fungal symbionts themselves. This chapter explores the factors which influence the colonization and life cycle of VAM fungi. Many soil-borne fungi have developed highly specialized methods of dispersal. The chapter discusses the active dissemination and passive dissemination where VAM fungi are moved by wind, water, or by soil microorganisms. In stripmined areas, rodent dissemination of VAM fungal propagules has been shown to increase the rate of revegetation. Soil animals such as mites or Collembola can feed on fungal spores or they may be ingested by worms. VAM fungal spores appear trapped on the mucilaginous surface of seeds within the capsule, and were probably wind disseminated.