Sampling and choosing cases in qualitative research: a realist approach starts with a bold assertion. The verb sampling does not adequately capture the work we do choosing cases in qualitative research. The noun sample is inadequate too. Our common understanding of sampling is that a sample is drawn from a predefined population and each unit within that population has a chance of being included greater than zero (Bowley, 1906; Gorard, 2007). These rules do not hold in a realist sampling strategy. In these 39 steps I will argue that cases are chosen and transformed throughout the research in a methodological strategy of casing. In short, casing is the working out of the relation between ideas and evidence to extend interpretation and explanation in the research (Ragin, 1992). But before I discuss the methodology and techniques of choosing cases in qualitative research the next six posts discuss my characterisation of realism.