The physicochemical needs of pharmaceutical research and development are described in this brief introductory chapter. The search for new drugs is very expensive. Since the universe of possible molecules is so large, search methods for drugs must be highly focused. Poor ADME (absorption, distribution, metabolism, excretion) properties of drug candidate molecules are often the causes of failures in drug development/clinical testing stages. These processes are multi-mechanistic, and are hard to predict accurately. Measurements of ADME-related properties, such as solubility, permeability, and ionization constants (charge state) are required. Medicinal chemists need to be more aware of the needs of such measurements.