Participants in public distributed computing do not find it easy to trust each other. The massive number of parties involved, their heterogeneous backgrounds, disparate goals and independent nature are not a good basis for the development of relationships through purely social mechanisms. This paper discusses the trust management issues that arise in the context of the XenoServer Open Platform: a public infrastructure for wide-area computing, capable of hosting tasks that span the full spectrum of distributed paradigms. We examine the meaning and necessity of trust in our platform, and present our trust management architecture, named XenoTrust. Our system allows participants of our platform to express their beliefs and advertise them, by submitting them to the system. It provides aggregate information about other participants’ beliefs, by supporting the deployment of rule-sets, defining how beliefs can be combined. XenoTrust follows the same design principles that we are using throughout the XenoServer project: it provides a flexible platform over which many of the interesting distributed trust management algorithms presented in the literature can be evaluated in a large-scale wide-area setting.