Pharmacokinetics is a science that has long been used in ascertaining the appropriate antimicrobial dose. It refers to the disposition of drugs in the body and includes absorption, bioavailability, distribution, protein binding, metabolism, and elimination. Pharmacodynamics is a newer science that relates to the interaction between the drug concentration at the site of action over time and the desired antimicrobial effect. This article reviews the principles of pharmacokinetics and pharmacodynamics as well as the clinical application of these two sciences to design antimicrobial dosing regimens for optimal results in individual patients.