The teacher education field has long recognized the importance of a robust teacher knowledge base that merges teachers' content knowledge and pedagogical knowledge to form pedagogical content knowledge (PCK). In this merging, both knowledge bases are transformed and refined. This chapter describes the nature of PCK needed to teach science, technology, engineering, and mathematics (STEM) through inquiry. Supported by this background and evidence from research, it then presents a vision for teacher awareness, growth, and deepening of PCK throughout their careers so as to strengthen their ability to enact STEM inquiry teaching. It weaves the development of this knowledge base with other teacher learning goals, such as incorporating social emotional learning. The ultimate goal is to strengthen teachers' abilities to teach all students with a content-rich, equitable, student-centered approach of engagement, inquiry, and problem-solving.