Recently, educational institutions have been urged to enable students to engage in social actions that address sustainability crises, underscoring the urgent need for environmental sustainability skills. This chapter focuses on important concepts regarding (environmental) sustainability and explores how these concepts intertwine with science education, influencing views and expectations of the domain, particularly in the context of transformative change. Furthermore, the chapter addresses the concept of environmental sustainability competence and the efforts to measure it (such as GreenComp) and to adapt these to education (such as the Environmental Sustainability Competence Toolbox). The chapter concludes with an overview of the Trends in International Mathematics and Science Study (TIMSS) 2023 Environmental Attitudes and Behaviors Framework and a discussion of how the three frameworks intertwine with one another to create a landscape for sustainability skills assessment.