The study investigates how higher education staff understand assessment, and the relationship between these understandings and their assessment practices. Nine individuals attended a workshop that guided them through the creation of a concept map about assessment, which was subsequently discussed in one-to-one semi-structured interviews. We found considerable variation in understanding of assessment, both between and within participants, and this appeared to be a consequence of the varied contexts within which assessment operates. Some assessment practices were highly complex, and at times closely entwined with teaching. In addition, individuals' practices helped to illuminate variation in how underlying concepts (e.g. assessment for learning) were understood. The approach supported the construction of the participants' understanding of assessment, and enabled the exploration of the interplay between thinking and reported practice, which were closely aligned. It also drew attention to the need to further develop methodologies which capture both the complexity of thinking about assessment and real-world assessment practices.