This part introduction presents an overview of the key concepts discussed in the subsequent chapters. The part presents examples of each of the several experiment designs and provides an introduction to some of the concepts and issues relevant to them. It discusses the concepts of design and analysis for experiments in a degree of detail sufficient for understanding the later material. The part is concerned with the number of individuals to be included in the research and the choice of appropriate design. It introduces designs, analyses, principles and techniques for comparing alternative conditions in experimental research. Experimental research is characterized by the researcher arranging an intervention in the lives of individuals in order to assess its impact on them. Experimental research requires both the proper experimental procedures and the appropriate sampling to ensure that inferential generalization is available. The main requirement for proper experimental procedures is that individuals be randomly allocated to the conditions.