There have been increasing calls in recent years to address the declining uptake of more challenging science, technology, engineering and mathematics (STEM) subjects in the senior years of schooling. This renewed focus on STEM in schools has been spearheaded at the highest levels, with the Australian Chief Scientist's 2013 strategic paper and the Prime Minister's recent innovation agenda positioning STEM education and occupations at the center of nation's future economy. Similar agendas are being pursued in other advanced economies. In this climate of increased national and international focus on STEM education, what do we know about young people's motivation to pursue STEM subjects at school? This paper presents the results of a scoping review of empirical research focused on investigating K-12 students' motivations for STEM subjects over five-year period from 2012-2015 (n = 48). The purpose of the review is to identify and synthesize the research over this period to determine the key factors driving selection of STEM subjects. Studies included in the review had a collective sample of 7,675 teachers and 44,871 students from 10 countries. Key factors influencing the choice of STEM subjects included individual influences, such as academic attainment, gender and career goals; school and teacher influences; family influences, such as having a parent in a STEM career; and economic influences such as the attractiveness of salaries in STEM fields. In the presentation, we provide an overview of the key findings for each of these thematic clusters. The findings of the existing literature will be of interest to careers and STEM educators at all levels. The gaps in the literature will be identified and presented as fruitful new areas for motivation research.