Developing the ability of students to think critically and systemically about sustainability issues is assessed in a variety of ways in different disciplines and institutions but there are few reports in the literature about what methods are the most successful. This paper discusses a range of assessment methods and characterises them in terms of Bloom′s taxonomy of cognitive processes. Examinations are efficient, standardisable and objective but are not suitable for measuring sustainability learning. They promote surface learning and fail to measure higher order cognitive processes characteristic of sustainability competence. Project based learning (PjBL) is a common approach in engineering disciplines as it mirrors engineering work. PjBL assessment tasks such as reports and presentations can be marked using taxonomies such as the SOLO taxonomy which measure the higher order cognitive processes that are required for sustainability competence. However, markers need a high level of skill to mark reliability with rubrics based on the SOLO taxonomy. Graphical tools such as concept maps are also effective in measuring higher order cognitive processes.