As teachers are central to digitalizing education, we summarize 40 years of research on their role in that process within a systematic umbrella review that includes 23 systematic reviews with a total of 1062 primary studies focusing technology integration and aspects of digital literacy. Our findings highlight the international acceptance of the TPACK framework as well as the need for a clear concept of digital literacy. It is unique that we identify and discuss parallels in developing teachers' digital literacy and integrating digital technologies in the teaching profession as well as barriers to those goals. We conclude by suggesting future directions for research and describing the implications for schools, teacher education, and institutions providing professional development to in-service teachers.