Teaching quantum mechanics conceptually faces significant challenges due to its inherently counterintuitive nature. As quantum physics is relatively new to secondary school curricula, and can be approached using various perspectives and topics – e.g. the historical, experimental-based, and spin first approach – research into students’ difficulties while learning QP is rather fragmented. During this presentation I will present several examples of research into students’ learning of quantum concepts. Additionally, I will substantiate the importance of international collaboration and highlight the efforts of a collaboration between European quantum education researchers, who are striving to gain insights into students’ learning and develop a quantum concept inventory.