Pharmacology is the study of exogenous chemicals including their actions on and movement throughout the body. As a science, it encompasses both pharmacodynamics and pharmacokinetics. Pharmacokinetics relates to the movement of chemical entities throughout the body. By understanding a medications pharmacokinetics, one understands what the body does to the drug. On the other hand pharmacodynamics is the science of what the drug does to the body or an infecting microorganism. Pharmacodynamics relates to the action of a drug in the body over a period of time. This chapter will also cover pharmaceutics, the science of pharmaceutical systems that focuses on drug preparations and dosage forms.