In order to discuss the role of mathematics education in developing students' STEM Capabilities and 21st Century skills, it is necessary to define what is meant by these terms given the extent to which they are broadly used in global contexts. A literature review aimed at providing clarity, through affording a concise interpretation of each term for the Australian context, enabled the development of a working framework for defining 21st Century skills and STEM capabilities. This paper provides working definitions and reports on initial findings from a larger three-phase study aimed at exploring secondary mathematics teachers' beliefs, attitudes and practices, towards the role mathematics education plays in developing students' STEM capabilities and 21st Century skills.