Prior language and literacy support from home, community and heritage language (HL) schools provides young HL learners with linguistic and metalinguistic foundations for language and literacy development (Chinen & Tucker "Heritage Language Journal" 3:27-59, 2005; Koda et al. Chinese as a heritage language: Fostering rooted world citizenry (pp. 125-135). University of Hawai'i, National Foreign Language Resource Center. 2008; Mori & Calder "Foreign Language Annals" 46:290-310, 2013). To date, few studies have explored the contribution of early language experiences to later HL literacy development. The current study aimed to investigate the role of learner-external and input-based language and literacy support in adult HL literacy development. Two hundred and nine Chinese as a heritage language (CHL) learners participated in the study. They completed a language and literacy background survey as well as a series of Chinese reading measurements. Drawing upon multivariate analyses, the results demonstrated that early language and literacy experiences as a whole contributed to later HL reading development. More specifically, language and literacy experiences in the community had a more salient effect on CHL literacy development than did home-based experiences. The study underscored the importance of crossing boundaries between learner-internal linguistic capacities and learner-external sociocultural contexts in HL literacy maintenance. [For the complete volume, "Crossing Boundaries in Researching, Understanding, and Improving Language Education: Essays in Honor of G. Richard Tucker. Educational Linguistics. Volume 58," see ED672546.]