This manual is a comprehensive resource for early drug discovery, providing guidelines for developing therapeutic hypotheses, validating targets and pathways, and establishing proof of concept criteria. It includes analyses of costs at various stages of drug development. The content encompasses critical decision-making points in New Chemical Entity (NCE) development, exploratory Investigational New Drug (IND) processes, and orphan drug designation. Furthermore, it delves into Drug Repurposing and drug delivery technologies, making it an invaluable guide for professionals initiating new drug discovery and development programs.