Scientifically sound network studies require the execution of large series of experiments. Researchers usually have to execute experiments manually, a labor-intensive and error-prone task, since there is no automation of the overall experimentation process. This task becomes especially hard on a distributed testbed and the researcher has to deal with additional challenges. In this paper we introduce the Distributed Embedded Systems Testbed Management System (DES-TBMS) for the automation of experimentation in wireless mesh networks and wireless sensor networks. DES-TBMS consists of several components including a domain specific language to describe and define experiments, a scheduler to manage and control experiments, a distributed monitoring system to gather system data, a visualization tool, and an evaluation tool to compute performance metrics from collected experiment data. Thus, DES-TBMS supports the researcher during the design, execution, and evaluation of experiments.