Pharmacokinetics, the study of drug absorption, distribution, metabolism, and excretion (ADME), is crucial in the drug development process. This review provides an in-depth analysis of the fundamental concepts and parameters of pharmacokinetics, compartmental and non compartmental models, and the integration of physiologically-based pharmacokinetic (PBPK) models. It explores preclinical pharmacokinetic studies, emphasizing in vitro and in vivo methodologies, predictive models for human pharmacokinetics, and ethical considerations. Clinical pharmacokinetic studies are discussed across various phases of clinical trials, highlighting dose escalation studies, drug-drug interaction assessments, and population pharmacokinetics.