Motility and chemotaxis are prerequisites for the ability of Azospirillum species to colonize the roots of diverse plants. In addition to chemotaxis, Azospirillum species have an oxidative metabolism adapted for microaerobic conditions. Aerotaxis represents a strong behavioral response of Azospirillum species that allow them to locate precise low oxygen concentrations in spatial gradients of oxygen/air. Chemotaxis signal transduction has been best characterized in A. brasilense strain Sp7. In this strain, two chemotaxis signaling systems and multiple accessory proteins control chemotaxis and aerotaxis. Chemotaxis responses in A. brasilense are tightly linked to metabolism and referred to as energy taxis. Both spatial and temporal gradient assays have been developed to measure chemotaxis and aerotaxis in A. brasilense, as well as in other Azospirillum species. The chemical-in-plug assays and its variations have been used to demonstrate A. brasilense chemotaxis attractant responses toward several organic compounds and plant root exudates as well as repellent responses away from redox active quinones or hydrogen peroxide. The root-in-pool assay represents yet another variation of the assay but uses plant roots as the source of chemoeffectors.