We present a formal framework for representing and reasoning about simultaneous changes of trust and belief. We introduce trust states, and we demonstrate how trust states can be explicitly updated by a new class of trust change operators. Trust change postulates are introduced, and a representation result is presented for these operators. We then demonstrate how we can use trust change operators to make implicit updates to trust in other agents, based on the accuracy of the reports provided by other agents. Broadly, agents are more strongly trusted when they provide reports that agree with observation and they are less strongly trusted when they provide reports that conflict with observation. We define combined trust-belief change operators that allow an agent to simultaneously update their trust in other agents while also revising their beliefs. Applications and implementations are considered.