Medicinal chemistry is a specialised science that has evolved to encompass a broad range of disciplines concerned with the identification, synthesis and development of drug-like compounds for therapeutic use. It needs a wide range of expertise, developed through years of training, dedication and learning from best practices in order to produce drugs that are good enough to enter clinical trials in patients. In the early days of drug discovery, medicinal chemists often optimised and developed compounds without much knowledge of the drug target or pathway in mind. It was a largely subjective process where chemistry-driven elaboration of chemical structures was undertaken and these compounds were often tested directly in vivo to optimise the biological response without much thought of ADMET properties. New technologies have had a huge impact on drug discovery since the mid 20th century. The early influence of experimental pharmacology, which was first employed to study drug side-effects, coupled with advances in cell biochemistry led to the identification of many enzymes and receptors as new drug targets, thus enabling medicinal chemists to develop compounds to interact selectively with targets for a wide range of therapeutic areas.