This book places much emphasis on the need to assure relevance by principles-guided objects design for the studies, which now remains conspicuously absent from epidemiologists’ concerns. And as for methods design, this book exposes the fallacies in the still-common ‘cohort’ and ‘case-control’ studies, defines the essentials of all etiogenetic studies, and then addresses the true options for design in this framework of shared essentials.