We present a logic which supports reasoning about an agent’s belief formation and belief change due to evidence provided by other agents in the society. We call this logic DEL-ES which stands for “Dynamic Epistemic Logic of Evidence Sources”. The term "evidence source" refers to an agent in the society who provides evidence to believe something to another agent. According to DEL-ES, if an agent has gathered a sufficient amount of evidence in support a given fact φ then, as a consequence, she should start to believe that φ is true. A sound and complete axiomatization for DEL-ES is given. We discuss some of its interesting properties and illustrate it in a concrete example from legal contexts.