This chapter defines heritage languages and motivates their study to understand linguistic diversity, language acquisition and variationist sociolinguistics. It outlines the goals of Heritage Language Variation and Change in Toronto (HLVC), the first project investigating variation in many heritage languages, unifying methods to describe the languages and push variationist sociolinguistic research beyond its monolingually oriented core and majority-language focus. It shows how this promotes heritage language vitality through research, training, and dissemination. It lays out overarching research questions that motivate the project:

• Do variation and change operate the same way in heritage and majority languages?

• How do we distinguish contact-induced variation, identity-related variation, and internal change?

• Do heritage varieties continue to evolve? Do they evolve in parallel with their homeland variety?

• When does a heritage variety acquire its own name?

• What features and structures are malleable?

• How consistent are patterns across languages?

• Are some speakers more innovative?

• Can attitudes affect ethnolinguistic vitality?

• How can we compare language usage rates among communities and among speakers?