Fungi belonging to the genera Trichoderma and Gliocladium are soil-borne saprophytes which have been used for industrial and agricultural applications for decades. Some strains produce enzymes and antibiotics while others are useful as biological agents for the protections of plants against pathogens. This first volume of two, gives a detailed account of the morphology and taxonomy of Trichoderma and Gliocladium, before discussing their ecology and basic biology. Molecular biological aspects examined include their genome and gene structure, genetic transformation and asexual genetics. A chapter on safety aspects is also included.