In treating microbial infections it is important that an effective concentration of antimicrobial drug be rapidly attained at the focus of infection. Drugs are administered as prepared dosage forms, such as parenteral preparations for injection, and tablets, capsules, suspensions, or pastes for oral administration. The chemical nature and related physicochemical properties largely govern the absorption, distribution and elimination, which refers to biotransformation and excretion, of antimicrobial agents. Since antimicrobial agents, like other drugs, are available as prepared dosage forms, the type and formulation of the dosage form determine the route of administration, the bioavailability and overall rate of elimination of the drug. This chapter discusses the pharmacokinetic properties of different antibacterial drug classes and their members, and factors affecting these properties. The major pharmacokinetic parameters that describe the disposition of a drug are the systemic (body) clearance (C1_B), volume of distribution (V_d) and half-life (t_1/2).