Abstract: Biocontrol with antagonistic microbes such as the fungus Trichoderma is one area of research. Trichoderma spp. are among the most common saprophytic fungi. Trichoderma spp. are well documented as effective biological control agents of plant diseases caused by both soilborne fungi and leaf- and fruit-infecting plant pathogenic fungi. Trichoderma spp. are often very fast growing and rapidly colonize substrates, thus excluding pathogens such as Fusarium spp. Several of these fungi are also parasitic to other fungi including plant pathogens. Trichoderma harzianum Rifai is an efficient biocontrol agent that is commercially produced to prevent development of several soil pathogenic fungi. T. harzianum alone or in combination with other Trichoderma species can be used in biological control of several plant diseases. An additional advantage for T. harzianum is that it increases growth in various plants. This review discussed biological control with Trichoderma spp. with emphasis on T. harzianum Biological Control with Trichoderma spp. with emphasis on T. harzianum and numerous mechanisms that Trichoderma spp. have evolved in attacking other fungi and enhancing plant and root growth