No two surveys are ever exactly the same (even when they are intended to be). They vary along so many dimensions (the identity and location of the target group, the way the data is gathered, the type of information sought, how frequently it is done and by whom) that it is not a simple task to classify them. This chapter offers an overarching definition of what a survey is, and moves on to differentiate surveys according to seven criteria: (a) the type of target population and the way it is sampled; (b) the topic of interest; (c) the sponsor and agency respectively funding and executing the survey; (d) the mode through which the survey is administered; (e) how frequently the respondents are surveyed; (f) the geographical scale and scope of the survey and (g) the reason why, and purpose for which, the data is being collected.