Bacterial growth is a complex process that involves numerous anabolic and catabolic reactions, which result in cell division. This chapter describes the various stages of bacterial growth under pure culture conditions and its relevance with growth in the environment. The increase in numbers or bacterial mass can be measured as a function of time under pure culture conditions, where the nutrients and environmental conditions are controlled. Several distinct growth phases can be observed within a growth curve such as the lag phase, the exponential or log phase, the stationary phase, and the death phase. Under batch conditions, the lag phase is the first phase that is characterized by zero growth. The second phase, exponential phase, is characterized by a period of the exponential growth, followed by the stationary phase in which there is no net growth because of several reasons such as nutrient depletion or accumulation of toxic waste products. The final phase of the growth curve is the death phase, characterized by a net loss of culturable cells. At high substrate concentrations, growth usually occurs at the maximum growth rate; however, this type of growth is unlikely to be found under natural conditions in a soil or water environment. The lag phase observed in a natural environment can be much longer than the lag phase normally observed in a batch culture. While the stationary phase is most likely of short duration, if it exists at all, the death phase can certainly be observed