The Science of Pharmaceutical Manufacturing – Book 1: Foundations of Defensible Pharmaceutics was written because, despite decades of guidelines, validations, SOPs, and inspections, oral solid dosage products continue to fail during scale-up, stability, bioequivalence, and regulatory review, not due to isolated mistakes but because of weak formulation architecture built on fragmented and empirical practices. Modern manufacturing still treats APIs, excipients, granulation, compression, coating, dissolution, and stability as separate steps rather than as one integrated system, allowing formulations to pass early testing yet collapse under time, humidity, stress, and scale. Material science is documented but rarely engineered, dissolution methods are designed to pass rather than discriminate, and stability is observed rather than predicted, leaving moisture migration, solid-state transitions, lubrication drift, and coating failures to surface only after damage is irreversible. This book exists because most references describe tests without explaining why systems fail despite passing them, and because no unified framework links particle engineering, granule architecture, tablet structure, moisture behavior, dissolution drift, and long-term performance into a defensible whole. Book 1 focuses on where failure is born, addressing material reactivity, hidden chemical instability, particle and granulation design, compression behavior, surface readiness, and moisture-driven drift, showing why shortcuts inevitably fail. Written for formulation scientists confronting unexplained variability, manufacturing teams battling recurring defects, quality leaders facing late-stage surprises, and regulatory professionals defending fragile logic, this volume provides the scientific foundation needed to build resilient products before enforcement begins, explaining why products fail today and preparing the ground for Book 2, where those failures are judged.