The question that animates this paper is whether a standardized protocol for measuring the amount and contours of intergenerational mobility in the United States might usefully be established. Thoughout our discussion, we understand "intergenerational mobility" to refer to the association between (a) the social standing of an individual’s family of origin (as assessed when the individual is growing up), and (b) the social standing of that same individual when she or he is an adult. This necessarily ambiguous definition begs as many questions as it resolves, but before attending to such ambiguities it's useful to lead off by rehearsing why social scientists should care, indeed care rather deeply, about how much mobility there is, whether it's increasing or declining over time, and whether the United States is at all distinctive in the amount of mobility it delivers. The various motivations underlying mobility research should naturally be borne in mind when considering whether a standardized protocol for measuring mobility should be devised.