There is no one best method for studying human development. Occasionally, theoreticians will promote one particular method as the ideal against which all others should be viewed as inadequate. Laboratory experimentation has sometimes been championed in this manner; naturalistic observation has also had its surprisingly vociferous adherents. When one considers, however, the astonishing breadth of subject matter studied by developmental psychologists, it is easier to defend the proposition that developmental researchers need a corresponding breadth of methodology. Studying the elderly will almost inevitably require different procedures from those suitable for studying infants. Hypotheses about the determinants of physical growth may necessitate the use of biochemical laboratory tests, whereas hypotheses about the development of moral reasoning probably would not. Even within a single topical domain—sex role differentiation for example—one researcher might focus on hormonal influences while another scientist might study cultural differences in how adults socialize boys and girls. In short, developmental psychology provides so diverse and rich a topical terrain that a very broad spectrum of methodology is necessary to do justice to it. The present chapter provides an overview of these methods. In the following three sections, we consider procedures by which data are gathered, including naturalistic observations, experiments, and correlational studies. Then, we consider the ways in which people are selected for study and the problem of obtaining representative individuals from whose behavior valid generalizations can be made. In the next two sections, we consider statistical issues; first general principles, then specifically developmental concerns. Finally, we consider ethical issues involved in performing research.