This book examines the digital competence of pre-service mathematics teachers. Six instruments were developed based on findings from a qualitative interview study exploring pre- and in-service teachers’ reasoning for selecting digital resources and a systematic literature review analyzing TPACK instruments from 2017 to 2023. The newly developed instruments, based on accepted competence and digital competence frameworks, address identified empirical and methodological gaps in assessing the digital competence of pre-service mathematics teachers. The latter are among the manuscript's research novelties and contributions to the research community. One of the newly developed instruments evaluates TPACK reasoning through open-text items that require reasoning for “selecting digital learning materials” (dLMs) for specific learning content, while considering the learners’ age and special needs. A second instrument applies the same approach to “selecting digital technologies” across different teaching phases and specific learning content, while also accounting for learners’ ages and special needs, but without specifying the digital technology. Pre-service teachers had to justify their choice of digital or non-digital technology in the latter instrument. In addition, multiple-choice items were developed to assess pre-service mathematics teachers’ TK, TCK, and TPK. All instruments were evaluated across six studies.