This paper examines the key issues at stake for national economies in increasing the number of PhDs to meet expected needs for human capital in science, technology and innovation using illustrations mainly from the European Commission's "Careers of Doctorate Holders" surveys on PhD labour market outcomes; it has been shown that PhD graduates might not be absorbed into employment as easily as previously anticipated. However, there is limited evidence of how PhD graduates mobilise and what determines their early career choices. Given the lack of evidence on demand, prioritisations for increasing the number of PhD graduates may not be in line with the perceived demand. Issues such as transitional barriers and disparities between career prospects and expectations are of primary concern. The conclusion is that there is a need to increase knowledge within the area to understand mobilisation patterns, to ensure continued attractiveness of doctoral education in the longer run and provide a research strategy to assist policymakers in their decision-making.