This chapter focuses on drugs of abuse and therapeutic drugs. Forensic toxicology involves the analysis of potentially toxic xenobiotic compounds in human tissues or in related material and the toxicological interpretation of the results. Forensic toxicology is influenced by the fact that the final reports produced may have to be introduced as evidence in a court of law. Thin-layer chromatography (TLC) has a creditable history in forensic toxicology, and numerous cases have been solved by this technique since Kirchner and Stahl demonstrated its potential in their books in the 1960s. In clinical forensic toxicology, urine is clearly the first specimen for screening analysis. Despite the obvious advantages of TLC, the technique has been criticized as being labor intensive and very much dependent on the skill and experience of the analyst. Classical liquid-liquid extraction is still widely utilized in TLC screening procedures. Visualization of the immobilized analytes, independent of time and place, is a unique advantage of TLC.