This study draws on the findings from a STEM education project to examine Hong Kong in-service primary school teachers’ perceived challenges in implementing STEM education, the support they received in STEM teacher professional development (STEM TPD), and their needs for future STEM TPD. The study engaged teacher professional development through a school-university partnership and adopted a practitioner research approach that aimed at enhancing primary school teachers’ professional capacity of designing STEM activities relevant to the Hong Kong curriculum, with an emphasis on the learning of crosscutting concepts and inquiry-based teaching. STEM TPD is aimed at collaborative curriculum development as an opportunity to foster active learning through co-creating curriculum materials among teachers and university facilitators. Twelve primary school teachers from various subject teaching backgrounds were interviewed. Semi-structured interviews were carried out to collect the teachers’ experiences with the STEM TPD and their views on the integration of cross-cutting concepts in designing STEM lessons. Findings of the study revealed teachers' perceived challenges during the preparation and teaching phases related to STEM instruction and lesson planning, limited resources, and other concerns embedded in broader contextual situations. While teachers reported to have received different types of support from the STEM TPD relating to the pedagogical knowledge of STEM, future directions for STEM TPD were expressed in relation to content components of STEM TPD, opportunities for authentic learning and first-hand experiences, and coherence. Finally, this chapter discusses areas that need to be resolved before a further enhancement in terms of quality and quantity of STEM lessons could be expected. Copyright © 2022 The Author(s).