This paper questions the appropriateness of a metaphor that is widely used by researchers and policy makers to represent a degree or career in Science, Technology, Engineering or Mathematics (STEM): that of a constantly narrowing pipeline. Such metaphor rests on two assumptions that, according to the authors, may be subject to criticisms: 1) a career in the STEM field includes a series of necessary, sequential benchmarks, and 2) the accumulation of all benchmarks is a sufficient requisite for such a career. On the basis of their review of the relevant literature, and new analyses of the National Educational Longitudinal Study of the Eighth-Grade Class of 1988, the authors claim that the pipeline metaphor not only does not adequately represent the process of becoming a scientist, but also conceals several important factors involved in it. Thus, they suggest a pathway metaphor, which in their view would better account for the multiple trajectories characterizing STEM degrees and careers and the heterogeneity of the STEM workforce.