We review the existing evidence, behavioral and neural, of infants' ability to encode repetition-('same') and diversity-('different') based regularities in speech. These studies show that, from birth, infants exhibit a robust capacity for learning repetition-based rules from speech (e.g. AAB or ABA, in which A = A). Further, the ability to generalize such repetition-based structures is not strictly language-specific, as infants' extract repetition-based structures from musical tones, animal pictures, abstract geometrical shapes, or faces under some conditions. However, this capacity is strongest when presented with speech or other communicative/meaningful stimuli. Additionally and importantly, recent brain-imaging studies suggest that by six months of age, infants also distinctly encode the notion of difference in speech stimuli. This is the youngest age at which this ability has been shown.