Ambient Assisted Living systems for the ageing and cognitively disabled do not exist in isolation. What characterizes such systems is the cooperation of several different stakeholders in the care process and the service platforms need to address this. This paper reports on our work in the EU IST MPOWER project where we have designed and implemented interoperability services based on patterns, service-oriented architectures, web services and XSDL transformations. The services we present are freely available as open source under the MIT license.