This chapter deals with an overview of solid phase extraction in biological, medical, environmental and forensics samples. First, the theory, principles, and history of SPE were discussed. Then, the application of SPE for separation and preconcentration of metal ions and organic species in environmental, medical, and biological samples was presented. The developments in SPE which led to the introduction of miniaturized techniques were also indicated. Next, the recent published studies were classified and explained to compare the various features of SPE techniques. One of the most dominant features of SPE is the application of different sorbents with various structures and diverse functional groups to improve the ability of SPE techniques.