The 21st-century explosion and decisive impact of digital media on education has highlighted the need for rethinking the required teacher knowledge for guiding students in taking advantage of improved technological affordances. The reformed teacher knowledge, called technological pedagogical content knowledge (TPCK or TPACK), is knowledge reflecting a dynamic equilibrium for the interaction of technology, pedagogy, and content. The intersection of these three knowledge domains reveals four additional subsets: technological pedagogical knowledge, technological content knowledge, pedagogical content knowledge and technological pedagogical content knowledge. The summation of these domains resides within the intellectual, social, and cultural contexts of education, to reveal the knowledge known as TPCK/TPACK. Teacher educators, researchers, and scholars have been and continue to be challenged with identifying appropriate experiences and programs for assessing and developing this teacher knowledge for integrating digital technologies as learning tools in reformed educational environments. Two questions guide this review of the literature surrounding the active, international scholarship and research toward understanding the nature of TPCK/TPACK and guiding the development of teachers’ TPCK/TPACK. The response to the first question describes the nature of this teacher knowledge for the digital age and how it differs from prior descriptions of teachers’ knowledge. The response to the second question explores the research and scholarship unveiling how this knowledge is developed and assessed at the pre-service and in-service teacher levels. From this scholarly work, three distinct views on the nature of TPCK/TPACK are proposed to explain various approaches in how this teacher knowledge is both developed and assessed in pre-service and in-service preparation programs. The integrated, heterogeneous vision recognizes the distinctness of the multiple subsets in the model and calls for specific preparation in each of the domains as key to developing the teacher knowledge for the digital age. The transformative, homogeneous vision considers the knowledge as a whole, composed through the integration of the multiple subset. Through the educational processes, the multiple subsets are rearranged, merged, organized, integrated and assimilated in such a way that none are any longer individually discernible. The third vision, called the distinctive vision, acknowledges the critical nature of the primary domains of pedagogy, content and technology and proposes the value of preparing teachers in each of these distinct domains. Supporting teachers for gaining the TPCK/TPACK-based knowledge, the preparation must respond to changes in content knowledge, pedagogical knowledge, and technological knowledge. These cumulative scholarly efforts provide a launchpad for future research focused on developing teachers’ knowledge for teaching in the digital age.