The development of biologics necessitates a comprehensive understanding of pharmacokinetics (PK) and pharmacodynamics (PD) due to their complexity. This chapter highlights the importance of quantitative pharmacology in integrating PKPD data to guide dosing, efficacy, and safety decisions. It covers essential aspects such as in vitro and in vivo pharmacology, bioanalytical methods, and drug exposure-based modeling for toxicology and first-in-human (FIH) dose estimation. Key considerations include drug metabolism and pharmacokinetics (DMPK), ADME processes, and immunogenicity risk assessment. Advances in bioanalytical assay technologies, including ligand binding assays (LBA), radio-immunoassays (RIA), and liquid chromatography-mass spectrometry (LC-MS/MS), are discussed for their role in measuring drug concentrations and ensuring therapeutic efficacy. The chapter also addresses the development and validation of bioanalytical methods, emphasizing the importance of accurate quantification for dose-response studies and the pharmacokinetics-pharmacodynamics (PK-PD) relationship.