The articles in this thematic issue document studies of grassroots actions in promoting multilingualism across different sectors of society as well as in different social and professional domains. In doing so, the contributors raise issues of the relevance of the notion of community in the age of superdiversity and the researcher's responsibility in researching multilingualism and superdiversity. Questions are asked as to whether empowerment and social change should be the ultimate goal of community-based research, and how applied linguistics research could impact on policy and practice. This introduction discusses the two related issues--the relevance of the notion of community in superdiversity, and the researcher's responsibility.