The Ph.D. research explores issues in the teaching of reasoning and proving. The topic has a central role at all levels of contemporary mathematics education, from K1 to K12, while over the years, there has been an increasing emphasis on understanding and constructing mathematical proofs. The candidate may analyze mathematics education in their own country (curricula, textbooks, school practice) in terms of the development of reasoning and proving skills and conduct surveys and teaching experiments to improve current teaching practices of these skills. The focus of the research may be on either student thinking or teacher behavior.