The IMS Question and Test Interoperability (QTI) standard identifies 16 different question types which may be used in online assessment. While some partial implementations exist, the R2Q2 project has developed a complete solution that renders and responds to all 16 question types as specified. In addition, care has been taken in the R2Q2 project to ensure that the solution produced will allow for future changes in the specification. The design of R2Q2 is described, the focus being on lessons learnt. We describe the architecture and the rationale of the internal web services and explain the approach taken in implementing the QTI specification, showing how the design allows for future tags to be added with the minimal of programming effort. The QTI standard has not had a great take-up in part due to the lack of tools. In the 2006 Joint Information Systems Committee Capital, three assessment projects were commissioned: item authoring, item banking and QTI-compliant test delivery. This article describes the "ASDEL" test delivery engine, focusing upon its architecture, its relation to the item authoring and item banking services, and the integration of the R2Q2 web service. (Contains 10 figures.)