This chapter discusses basic concepts in human development including developmental periods from prenatal to adolescence. It covers qualitative and quantitative changes, continuous vs discontinuous development, and influences on development such as genetics, environment, and developmental history. The chapter also summarizes several influential historical theories on development from Locke, Rousseau, and Darwin. Modern cognitive and social-emotional theories are discussed, including those from Piaget, Vygotsky, Freud/Erikson, and Bowlby. Research goals and considerations are outlined.