Wireless Sensor Networks (WSNs) consist of several autonomous resource constrained sensor nodes distributed over a geographical area. The sensor nodes can measure, for instance humidity, temperature or vibration. Therefore, these networks can be deployed in many different types of dynamic environments. Traditionally, Medium Access Control (MAC) protocols used in WSNs are implemented in a monolithic fashion with tight coupling to the underlying hardware. Although this approach of design and implementation can usually make full use of the capability of the underlying hardware, theMACsolution is static and provides satisfying performance only under the pre-defined conditions. However, as application requirements and network conditions may change, adaptability and reconfigurability of MAC protocols are desired. In this thesis, we have designed and implemented a toolchain which enables runtimeMACprotocol reconfiguration for WSNs. The toolchain has been implemented in TinyOS using component-based design and hardware independence, allowing users to develop MAC solutions for WSNs, execute and reconfigure them in many platforms. Finally, a user is able to interact with the sensor node through a user interface developed in Java. Furthermore, this toolchain has been enhanced by the features introduced in [1] to enable also simplifying the design of MAC protocols, allowing non-specific sensors users to implement and finally execute and reconfigure them in sensor nodes. The toolchain has been compared to monolithic implementations in terms of execution time and reconfiguration costs. The results show that the toolchain enables fast runtime reconfiguration of MAC protocols with an quantify execution time overhead. Our toolchain saves from 26% up to 98% the time needed to reconfigure a MAC protocol compared to the monolithic approach.