Significant controversy exists about the nature of phonological awareness, a causal variable in reading acquisition. In 4 studies that included 202 5- to 6-year-old children studied longitudinally for 3 years, 123 2- to 5-year-old children, 38 4-year-old children studied longitudinally for 2 years, and 826 4- to 7-year-old children, the authors examined the relation of sensitivity to rhyme with other forms of phonological awareness. Rhyme sensitivity was indistinguishable from phonemic awareness, segmemal awareness, and global phonological sensitivity in younger children. Rhyme sensitivity was distinguishable, although highly correlated, with these phonological skills in older children. Rhyme sensitivity was highly predictive of these other phonological skills. Children's sensitivity to different linguistic units seems best conceptualized as a single underlying ability