This paper reviews some basic elements of musical structure, drawing from work in traditional and cognitive musicology, ethnomusicology, psychology, and generative textsetting. Music features two different hierarchical representational components that can both be visualised in grid notation: metrical structure and event hierarchies (also referred to as Time-Span Reduction). Metrical structure is an abstract pattern of stronger and weaker points in time that form a temporal 'scaffold' against which auditory events occur, but is partly independent from those occurring events. Event hierarchies encode the constituency (referred to as grouping) and prominence of actually-occurring musical events. Basic principles of these components are illustrated with examples from Western children's, folk, and popular song. The need for both metrical hierarchy and event hierarchy is illustrated using mismatches between metrical and rhythmic structure. The formal, conceptual, and empirical features of musical metre are quite different from linguistic stress and prosody, despite the frequent analogies drawn between them. Event hierarchies, on the other hand, are shown to resemble linguistic prosodic structure with regard to all of these features.