Unified mechanistic treatment of PK, PD, and DDI concepts Conventional resources often present PK, PD, and DDI as separate domains, offering empirical relationships without detailing underlying assumptions. Concepts in Pharmacokinetics, Pharmacodynamics, and Drug-Drug Interactions unifies all three disciplines within a single volume, anchoring each in biophysical principles. Written by a pharmaceutical scientist, this work supports coherent, assumption-aware model development across the drug development value chain. The content is structured into eight sections covering biophysical fundamentals, pharmacokinetic principles, absorption, distribution, elimination, pharmacokinetic forecasting, pharmacodynamic receptor binding and in vivo pharmacology, and mechanisms of drug?drug interactions involving both PK- and PD-based pathways. This structure clarifies interdependencies across domains that are often obscured in fragmented treatments, supporting more transparent pharmacological modeling. Key features include: Systematic elucidation of simplifications and assumptions embedded in standard PK, PD, and DDI models used across the field Mechanistic grounding in binding dynamics, mass transfer principles, and reaction kinetics that underpin quantitative pharmacology frameworks Cross-disciplinary applicability spanning pharmaceutical sciences, clinical pharmacology, and regulatory modeling in diverse professional settings Support for model-informed drug development through frameworks that enhance predictive accuracy and transparent decision-making throughout the pipeline Integrated coverage eliminating the need to consult multiple separate references when developing or evaluating pharmacological models Pharmaceutical scientists, clinical pharmacologists, regulatory modelers, and advanced graduate students working across DMPK disciplines will find this volume a substantive single-source reference. By unifying PK, PD, and DDI within a biophysical framework, it equips practitioners to build more robust and transparent pharmacological models.