Marine chemistry is a matter of scientific interest from many points of view, above all those related to environmental contamination. Nevertheless, they are some problems in the analysis of marine samples (seawater, marine animals, macroalgaes, sediments, etc.) such as high salt content of the matrix, low analyte(s) concentrations, sample dissolution, etc., which results in complicated and tedious sample pre-treatments. However, many of these drawbacks can be solved by the application of automatic methods based on flow injection analysis (FIA). The concept of FIA was first proposed in 1975, and from this date, many researchers have proposed analytical methodologies involving FIA to determine organic and inorganic analytes in marine samples. FIA methods allow automatic handling of sample and reagent solutions with a strict control of reaction parameters. Furthermore, a FIA manifold is robust in shipboard laboratories, with the advantage of minimal sample handling and thus low exposure to contamination. Flow injection methodologies improve off-line sample pre-treatments, between others: preconcentration by using chelating resins, solid-phase extraction, and lixiviation procedures, resulting in rapid, efficient, safety, inexpensive and environmentally acceptable methodologies for the determination of several analytes in marine samples. Other advantages of FI methodologies are an important contribution to achieve a miniaturised, automatic, and green Analytical Chemistry. This book aims to cover the most important advances in the analysis of marine samples employing flow injection methodologies and will be a tool for all chemists who perform analyses on a routine basis in the environmental field.