This chapter describes an approach to assessment task design and delivery from the Assessment and Teaching of 21st Century Skills project (ATC21S). ATC21S is an example of an innovative, international, multi-stakeholder partnership involving industry, academics, governments, and educators that is aimed at shifting the direction of assessment and teaching towards a model more suited to the development of skills that students need in the 21st century. Within ATC21S, assessment design and delivery is just one component of a holistic framework in which assessment, teaching, resourcing, and policy work in unison to improve student outcomes. This chapter outlines this developmental framework and the impetus for ATC21S and partnerships which drive and support the project, and sets the scene for dealing with performance measurement issues – how can we tell that people have learned anything? The focus of the chapter is on the technology-based design and delivery of assessments of one of the key skill areas of interest in the project - collaborative problem solving.