In this slender text, Aikin, a researcher for Kaiser Permanente, identifies the scientific theories, properties, and characteristics of causation in biology, medicine, and epidemiology. He outlines the pathways of disease, analyzing casual systems and variables and describing current models, tools, and examples. Applying the constructive approaches of Rothman and Mackie to Down's syndrome, obesity, and gestational diabetes, the book constructs probability models for the visualization of causal pathways.