In the borderland between mathematics education and adult education a new research field has been cultivated, and an international research forum is formed: Adults Learning Mathematics. The subject area encompasses formal adult mathematics education as well as adults’ non-formal mathematics learning in the communities of everyday practice, e.g. the workplace. The key concept is numeracy and the problem field is related to mathematics and lifelong education. Danish researchers have played a role with their theoretical and empirical studies and in their engagement in the international community of research and in international networks and projects. This article presents an overview of Danish research in adults learning mathematics with a focus on the interplay between research and education. These are the key issues: What do adults know; why do adults (not) learn mathematics; why teach mathematics to adults; and how to teach or what is “best practice” in adult mathematics education. The epistemological concept of problematique is used as an analytical tool in this overview.