Project MERIA has been proposed on the initiative of mathematicians and mathematics educators from Croatia, Slovenia, Denmark and the Netherlands to improve mathematics education. The “exercise paradigm” in many everyday practices of teaching mathematics (including upper secondary and even university courses) may be a main factor that shapes the common students’ impression of mathematics as uninteresting (tedious routine work), irrelevant (at least to them) and useless (except to pass an exam). The alternative proposed and pursued in this project can be roughly characterized as inquiry based mathematics teaching (IBMT), where exercises are replaced by “inquiry activities” of various types. The project aimed to be based on serious and visionary research on how to realize the aforementioned tasks.The main objectives of the project are: 1) promoting IBMT based on the theoretical approaches of Theory of Didactical Situations (TDS) and Realistic Mathematics Education (RME), 2) providing systematic and overarching support to the curriculum, by creating a repository of mathematical showcase scenarios and modules for secondary schools, 3) upgrading teaching skills of in-service teachers so that they have necessary competences for dealing with diversified groups of learners by using learner-centred approaches and methods, 4) strengthening cooperation and flow of ideas between educational and research institutions dealing with mathematics education at different levels as well as transfer of innovative practices at European level. The project team consisted of mathematicians and researchers in mathematics education (university professors), mathematics teachers and teacher trainers from 11 institutions (6 faculties or universities, 2 high schools, 2 professional associations and 1 national institute for education). Jointly, the project partners designed six intellectual outputs: Practical Guide to IBMT, Template for Teaching Scenarios and Modules, collection of six scenarios and modules, Workshop Guide and Project Impact Analysis. The team has worked closely with teachers from 13 associated schools in all four countries. The role of the associated schools was to try out the teaching materials and provide feedback on its usability, as well as to participate in the interviews providing a basis for the understanding of teachers' needs and barriers for implementing IBMT. In the final phase of the project, we have organized cycles of professional development for mathematics teachers in Croatia, Slovenia and Denmark. A cycle consisted of two workshops, between which the teachers used teaching materials in their own classrooms. Teachers collaborated, discussed and reflected on the implementation which makes a very rare and very precious form of professional development. Students have evaluated lessons based on MERIA scenarios as interesting and engaging, while teachers describe materials as concrete, detailed and useable. Teachers have in particular pointed out that this type of material is rare and needed, in particular due to current curriculum reforms in Denmark and Croatia which focus more on problem solving and active learning. On the other hand, we have learned that teachers lack time and experience to design their own innovative materials. Hence, an interactive repository has been set up on the project web page for teachers to share their materials and further efforts of the project team will be made to develop design principles for tasks that support IBMT. At the end of the project, a final conference with teachers from all four countries was organized at the Faculty of Science. At the conference, all intellectual outputs were disseminated, plenary talks were given that extend the theoretical frameworks used in the project, workshops presenting teachers' new ideas was organized and finally, a public lesson was given by one of the teachers form the team. For a majority of participants it was a first such experience, which emphasized the importance of collaboration between teachers aimed at improving the teaching practices. Understanding the ways in which in-service teachers improv their skills and collaborate provided an idea for a follow-up project that has been also granted by the Erasmus+ programme. This project is called Teachers' Inquiry in Mathematics Education (TIME) and it will focus on small communities of teachers using the method of Lesson Study to jointly experiment and improve the quality of teaching in their schools.