This material includes the set of slides that are used in the teaching of the group in English of Pharmaceutical Chemistry (code 34066), an annual subject taught in the third year of the Degree in Pharmacy. The content deals not only with the drugs’ origin, development and design, but also with the study of the factors to be considered as regards their action. The design of drugs originally focused mainly on simple chemical modifications of the molecules of natural origin but current design trends are based on the study of the interactions of drugs with their target structures at molecular level. Therefore, from the knowledge of many target molecules in drug action, such as enzymes, membrane receptors and nucleic acids, a part of the design of new drugs is currently based on drug-target interactions. Through the study of the active ingredients of medicines from a chemical point of view we will be able to determine the relationship between their chemical structure and physicochemical properties, and their biological response, with the ultimate goal of providing the knowledge required for the creation of new drugs. In the first unit, important definitions on the topic have been given. Also, drug classification criteria and basic concepts about drug nomenclature as well as some features about the pharmaceutical industry have been included. The second section is mainly devoted to the study of the targets regarding their chemical nature, and some examples of drug-target interactions have been highlighted. The third unit includes some basic concepts in drug action, with a special focus on the relationships between the physicochemical properties of drugs and their in vivo pharmacological activity. Solubility in water, degree of ionization and lipid solubility as well as molecular shape and stereochemistry have been more thoroughly explained. The influence of these properties on pharmacokinetics and pharmacodynamics has also been considered. In the next section, dealing with drug metabolism, phase I and phase II biotransformations have been reviewed from a chemical point of view, focusing on the type of reactions an organic molecule can undergo in our body depending on its chemical structure. In addition, the study of bioprecursors and prodrugs as “latent active compounds”, as well as soft and hard drugs, has also been included as interesting strategies in the design of safer and more active compounds based on previous ones. Unit 5 covers the main strategies used in the design and development of new drugs, from the serendipitous discovery towards a more rational approach. Besides, pharmacomodulation techniques have also been covered so that they allow structure optimization by chemical modifications from lead compounds. Some examples of receptor activation and/or deactivation and different types of enzyme inhibitors have been given as a way to illustrate the success of the target-based approach in drug design. Finally, some basic ideas about the use of molecular modelling and computer-based drug design have also been included. The last part (unit 6) is an extension of the previous one and deals with the methods used to correlate physical and chemical parameters with biological activity and it shows how quantitative structure-biological activity relationships (QSAR) can help us in the design of new active compounds.