The use of experimental designs is an extremely powerful scientific methodology for directly testing casual relationships among variables. Experiments that are embedded within probability-based survey samples make for a particularly valuable research method as they combine the ability to more confidently draw causal attributions based on a true experimental design that is used with the ability to generalize the results of an experiment with a known degree of confidence to the target population which the survey has sampled. Cook and Campbell discuss how the four forms of validity in the Campbell and Stanley framework are interrelated. This chapter discusses how they interrelate to the phraseology and conceptualizations common to survey research. It deals with more explication about the interrelationships among the different types of validities and errors, followed by an even more detailed review of internal validity and external validity.