Project TIME has contributed to the paper discussing development of Lesson Study in Denmark. Lesson Study in mathematics has a relatively short history in Denmark (about 15 years) and it is still not widely implemented. What can be learned from the first experiences in this relatively privileged small country? In this paper, the authors outline the situation in three main institutional contexts, namely basic school (primary and lower secondary), high school (upper secondary) and teacher training in university colleges, while trying to answer the following questions: what motivated the initiatives to introduce Lesson Study to mathematics teachers? What obstacles and results are experienced? In the final section, the authors summarize their answers with a focus on what may be of interest in similar contexts outside of Denmark.