The cell is the fundamental unit of life, so an understanding of cell structure and function is indispensible for biologists. All cells share core components such as a cell membrane, a genome, and macromolecular machines to replicate, transcribe, and translate the genome. This chapter covers these core structures as well as some specialized structures found in only some species. The focus is on how structure correlates with function; for example, how does the structure of the cell membrane allow selective transport and energy production? These structural studies have medical applications, as many antibiotics work by inhibiting the function of cell structures; for example, penicillin inhibits cell wall formation and many antibiotics target ribosomes. An emphasis is placed on various tools researchers use to determine cell structure and function, such as subcellular fractionation, imaging technologies, and genetic analyses. Experiments are presented throughout the chapter to show how we know what we know. This chapter is a launching pad to many other chapters throughout the text. Subsequent chapters will refer back to this fundamental knowledge and expand on it, so make sure you are quite comfortable with this material.