This document provides an overview of the key concepts and approaches used in the scientific study of human development across the lifespan. It discusses the nature vs nurture debate, critical and sensitive periods of development, lifespan perspectives including multidirectionality and multicontextuality, and major theories of development including psychoanalytic, behaviorist, cognitive, and systems theories. It also outlines the scientific method and approaches used in development research such as observation, experimentation, surveys, cross-sectional and longitudinal designs, and cautions regarding correlation vs causation. Research ethics around informed consent and protecting participants are also briefly discussed.