This chapter focuses on flow injection analysis (FIA), a technique introduced in the mid-1970s for automated sample analysis. FIA involves injecting samples into a flowing carrier stream, leading to t...This chapter focuses on flow injection analysis (FIA), a technique introduced in the mid-1970s for automated sample analysis. FIA involves injecting samples into a flowing carrier stream, leading to transient signals at a detector, influenced by physical and chemical processes. The chapter outlines FIA's theory, describing components like propelling units, injectors, detectors, and transport systems. Applications span environmental and clinical analyses.