The success and competitive edge of enterprises has become increasingly dependent on the enterprises’ agility to become members in business networks that support their own business strategies. Therefore, integration solutions with their well-weathered strategic networks are no longer sufficient. Instead, there is need for more open business service ecosystems where previously unknown services and partnerships can be utilized. The ecosystem is to be supported with infrastructure services to solve the evident problems of semantic and pragmatic interoperability and collaboration-governing contract management. Furthermore, the ecosystem must support the creation of trust relationships with previously unknown partners, and reacting to encountered breaches of trust within collaborations. This paper proposes a trust management system where autonomous enterprises make automated, private trust decisions about their membership in each collaboration separately, while taking advantage of globally shared reputation of business peers in earlier collaborations. The trust decisions are adjustable to different and changing business situations.