Trust and reputation are two related, but different concepts. Various trust and reputation mechanisms have been proposed for centralized systems and for decentralized systems. Since trust is multi-faceted, even in the same context, agents / peers still need to develop differentiated trust in different aspects of other peers' behaviors. The agent's or peer's needs are different in different situations. Depending on the situation, an agent / peer may need to consider its trust in a specific aspect of another peer's capability or in multiple aspects. Bayesian networks provide a flexible method to present differentiated trust and combine different aspects of trust.