The pollution problem of the environment has reached a level that serves as a potential threat not only to the health of our environment but also to the entire population. Any undesirable and toxic chemical, commodity, organism, or other object present in the environment may be considered an environmental pollutant. Metal ions enter into the environment through natural or anthropogenic activities. Among the various metal ions, transition metals and some lanthanides and actinides are harmful and toxic. The speciation of a metal ion in the environment is a difficult job, as the concentrations of heavy metals in the environment are generally very low. Different analytical methods used for metal ion speciation include spectroscopic, polarographic, chromatographic, and electrochemical methods. The chromatographic methods involve the use of gas or liquid separately as the mobile phases. The most important liquid chromatographic methods are high-performance liquid chromatography and ion chromatography. The chapter also presents an overview of the key concepts discussed in this book.