Segmentation in biology refers to the division of some animal and plant body plans into a series of repetitive segments. This article focuses on the segmentation of animal body plans, specifically using the examples of the phyla Arthropoda, Chordata, and Annelida. These three phyla form segments by using a “growth zone” to direct and define the segments. While all three have a generally segmented body plan and use a “growth zone,” they use different mechanisms for generating this patterning. Even within these phyla, different organisms have different mechanisms for segmenting the body. Segmentation of the body plan is important for allowing different regions of the body to develop differentially for different uses.