This Report provides a factual account of the discussions during the 27 – 28 March 2007 STCA & ACAS Interactions and Interoperability Workshop. As such, the Report contains a strong stakeholder message that is expected to influence the work programmes of the organisers of this workshop, the Swiss Federal Department of the Environment, Transport, Energy and Communication/Civil Aviation Safety Office (DETEC/CASO) and EUROCONTROL.