As the demand for online learning environments grow in higher education, so does the need for systematic application of learning and educational theory to the design, development and delivery of assessment strategies within these environments. However, there is little guidance in the form of principled design frameworks that can assist the design practitioner in the development of online assessment strategies. From four cases, we have identified six design principles that represent the collective experience of our team of design practitioners in creating assessment strategies for online teaching and learning environments; (a) technology affordances, (b) alignment of objectives with assessment, (c) discipline-specific practices and approaches, (d) meaningful and timely feedback, (e) authenticity and transferability and (f) transparency of assessment criteria. We present in-situ qualitative case studies that articulate how these principles have informed our design practice in online assessment strategy development. (Contains 6 figures.)