The innate capacities and developmental mechanisms involved in infants’ acquisition of their native language are basic topics in speech perception development. Developmental trends regarding infants’ perceptions of phonetic segments have been well documented over the past decades; however, studies on the development of “lexical tones,” which represent a phonetic unit unique to tonal languages, have only begun to emerge in the last decade. This chapter reviews studies on tonal perception development in infants learning a tonal language (e.g., Mandarin and Cantonese) or a nontonal-language (e.g., English and Dutch). These studies have demonstrated that infants learning a nontonal-language are able to discriminate tonal contrasts at the age of 4–6 months, but they cannot easily distinguish the same tonal contrasts at the age of 9–12 months. Conversely, infants exposed to a tonal language exhibited superior ability to discriminate tonal contrasts at the age of approximately 12 months. The trend of lexical-tone learning is similar to that by which infants learn phonetic segments. Developmental factors for tonal perception include experience listening to the native language, the acoustic salience of lexical tones, statistical learning, musical tone exposure, and referential word learning.