This article proposes a theory of flow (the rapped vocals of hip-hop music) segmentation, phrasing, and meter that considers the way linguistic, syntactic, articulative, and corporeal aspects of rapping engage with vocal rhythm and its grouping structures. While flow is organized into phrases, hip-hop beats (the sampled or instrumental accompaniment) typically express a periodic, looped, highly repetitive metric structure against which these flow phrases operate. The patterns of metric alignment and non-alignment generated between flow and beat layers imbue hip-hop music with nuanced variety, especially at sub-sectional formal levels.