The aim of this thesis was to understand and explore how a strategic sustainable development perspective can be integrated in product sustainability performance assessment practices. Based on an interactive qualitative research approach, three studies were conducted. The first study reviewed early-phase assessment approaches available in literature and found that although many approaches exist, a systemic and strategic perspective was often not completely addressed. Six criteria were therefore developed to support integration of such a perspective in assessment approaches. The second study focused on two EU policy instruments and while both instruments presented opportunities to incentivize and support product sustainability performance assessments, they provide limited support for considering the full socio-ecological systems perspective and long-term strategic decision-making. The third study used a multi-case study to deepen the understanding of how product developing companies work with and use product sustainability performance assessments. The findings showed that product sustainability performance was assessed, but companies face challenges and their practices were not fully aligned with a strategic sustainable development perspective. Ten propositions were formulated for what must be considered to integrate such a perspective in company practices, so that assessments can function as strategic decision-support for developing products that can contribute to society’s transition towards sustainability in ways that benefit the own organization. Together, the three studies highlight the need to develop both individual assessment approaches and the surrounding practices in which they are embedded to support effective integration of a strategic sustainable development perspective into assessment practices in the product development process.