Chemistry is the science and art of creating new molecules. The ability of natural and non-natural substances to interact with biological processes and influence their course is fundamental to modern medicine and to the whole concept of pharmacology. Bioactive substances were sometimes identified serendipitously in natural extracts and became a legacy of traditional medicine. Today, compounds that interact with biological processes and can become drugs are carefully designed and constructed to fulfill rigorous criteria of efficacy, selectivity and safety. Chemists are active in all areas of drug discovery, from target identification and validation all the way through to the supply of active pharmaceutical ingredients for clinical studies.