Simultaneous determination of multiple components by the flow injection technique (MC FIA) of various configurations with a single detector (single or multichannel), or with several detectors in series or in parallel, is described. Exclusive instrumental modules, i.e., multifunctional valves, special detectors, and their combinations are also given. Special techniques employing liquid-liquid extraction, membrane separation, packed microcolumn reactors, immobilized enzyme reactors, etc. are discussed. The applicability of MC FIA in simultaneous determination and speciation of metal ions, inorganic anions, and organic compounds in diverse samples is also presented.