Despite the range of varieties of Han Chinese, Mandarin is the most widely studied variety in research on Chinese as a heritage language (CHL) around the world. To better understand the role of other varieties of Han Chinese in addition to Mandarin, this article presents a synthesis of research on the learning of Chinese varieties in formal and informal contexts worldwide. We reviewed 25 empirical studies in CHL learning worldwide to examine 1) the definition of CHL learning, 2) varieties of Chinese as heritage languages, 3) theoretical frameworks, and 4) research trends in formal CHL learning programs, as well as informal CHL learning in families and communities. Mandarin was found to be the most studied variety, while varieties such as Cantonese, Hakka, and Hokkien are less frequently investigated. The findings highlight research gaps related to the research contexts, language varieties, and theoretical frameworks in CHL learning. This review points to the need for the exploration of CHL learners in non-English-speaking regions, wider representation of Chinese varieties in CHL research, and inclusion of a broader range of formal and informal learning contexts in the CHL research.