This chapter explains the significance of the cell in development. Any consideration of human reproduction, genetics, and development should begin with the cell. The interactions of cells during development include the formation of junctions between cells. The chapter explains s simple diagram of a cell showing the nucleus, cytoplasm, and plasma membrane and the general role of each. The nucleus is found within the cytoplasm of the cell and generally has a spherical shape. The cytoplasm is the material that fills the space between the nuclear membrane and the plasma membrane. The chapter describes each of the following parts of the nucleus and provides their functions in cells: chromosomes, chromatin, genes, nuclear membrane, and nuclear pores. It also provides the general cellular roles of the following cytoplasmic organelles and a specific function of each in human development: mitochondria, Golgi bodies, lysosomes, and centrioles.