Critical Mathematics Education can be understood as an expression of concerns regarding mathematics education and the different sociopolitical roles it can play in society. These concerns encompass what happens in mathematics classrooms and the opportunities in students’ future lives; socioeconomic exploitation, racism, sexism, homophobia, xenophobia, and violence; mathematics itself—not only the school-taught variety but also the mathematics used in different contexts and jobs—, which directly impacts people’s lives; democracy and social justice; and the connection of mathematics education with issues such as equity, inclusion, power relations, students’ and teachers’ foregrounds, dialogue, among others. Educational approaches developed from the perspective of Critical Mathematics Education aim to go beyond mere number manipulation and solving of application problems in the classroom. They seek to provide students with opportunities to question the notions of exactness and absolute rationality of mathematics while providing them with mathematical skills to understand the political structures of inequality, social injustice practices, and mechanisms of oppression, and to act towards transforming the world. One such educational approach involves working with Landscapes of Investigation which are learning environments where students are invited to engage in tasks offering opportunities to: (a) participate in exploratory and investigative processes, including activities such as developing lines of reasoning, conjecturing, testing hypotheses, conducting experiments, proposing and defending ideas, constructing new hypotheses, or creating models; and (b) critically explore and reflect on sociopolitical issues, many of which are controversial. In the context of primary school teacher education, existing literature indicates that practices have often failed to fully capitalise on the potential of approaches like landscapes of investigation. In this regard, at the research level, the project Li-Primary Teachers aimed to understand, from the perspective of Critical Mathematics Education, how primary school teachers plan and implement Landscapes of Investigation with their students within a context of in-service professional education and development. The project had the following specific objectives: (a) to review high-impact mathematics education journals to examine the current state of research on the in-service primary school teacher education; (b) to analyse how primary school teachers learn, through continuous professional development, to design tasks based on Landscapes of Investigation focused on exploring social issues; (c) to identify teacher education dynamics that support professional learning; and (d) to examine possible changes in teachers’ didactical conceptions of mathematics based on their involvement in in-service professional development. The data were collected during a year-long in-service teacher education programme involving 12 Portuguese primary school teachers. This programme included stages of study and experimentation, planning and enacting of Landscapes of Investigation with primary school students, and collective reflection on the work undertaken. Interviews were also conducted after the conclusion of the teacher education programme.