"The Mathematics Teacher in the Digital Era" is a scholarly book that focuses on the initial training and continuous professional development of mathematics educators. It aims to explore and promote the possibilities of using educational technology in mathematics instruction. The book brings together contributions from leading scholars in the field and offers a mix of research articles and descriptive texts. In the introductory chapter, John Mason invites readers to engage with various mathematical tasks that highlight essential features of technology-supported mathematical activities. The book is divided into three main sections, examining current practices in the use of digital technologies in teaching as well as the development of more effective practices. It considers various research perspectives, including Grounded Theory and enactivist theory. Furthermore, it presents metacognitive reflections on research in this area by contrasting different approaches and proposing connecting elements.