Chemotaxis, the directed movement of microorganisms in response to chemical gradients, plays a pivotal role in microbial ecology. This article provides a comprehensive review of mathematical models that couple chemotaxis with reaction dynamics to describe microbial population behavior. We discuss how such chemotaxis–reaction models capture essential ecological phenomena, from nutrient foraging and biofilm formation to inter-species competition and environmental processes. Key model formulations, starting from the classical Keller--Segel system, are presented alongside extensions incorporating multiple species, complex reaction terms, and fluid flow coupling. We survey rigorous mathematical... More >