While some accounts of syllable weight deny a role for onsets, onset-sensitive weight criteria have received renewed attention in recent years (e.g. Gordon 2005, Topintzi 2010). This article presents new evidence supporting onsets as factors in weight. First, in complex stress systems such as those of English and Russian, onset length is a significant attractor of stress both in the lexicon and in nonce probes. This effect is highly systematic and unlikely, it is argued, to be driven by analogy alone. Second, in flexible quantitative meters (e.g. in Sanskrit), poets preferentially align longer onsets with heavier metrical positions, all else being equal. A theory of syllable weight is proposed in which the domain of weight begins not with the rime but with the p-center (perceptual center) of the syllable, which is perturbed by properties of the onset. While onset effects are apparently universal in gradient weight systems, they are weak enough to be usually eclipsed by the structure of the rime under categorization. This proposal therefore motivates both the existence of onset weight effects and the subordination of the onset to the rime with respect to weight.*