The ecological relationships that organisms establish with others are broad and diverse, those interactions can be considered as a continuum spectrum, ranging from beneficial to detrimental outcomes. Biological control defined as the conscious use of living beneficial organisms for the control of pests is a key ecosystem service for sustainable crop production, where natural enemies play a central role in limiting damage from pests. In this chapter we discuss the impact of plant pathogenic microorganisms and pests insects, introduce general concepts, as well as, biotic interactions involving pests and biological control agents in agro-ecosystems and the major approaches for biological control.