Wireless Sensor Networks are a relatively new technology, actively researched by many groups around the world. This project is a continuation of a former project at the University of Oslo, focusing on WirelessHART. Our aim were to gain an understanding of the WirelessHART protocol, before further developing and improving the implementation.This report provides the reader with an introduction to Wireless Sensor Networks to build a general knowledge. This knowledge is then used to help describe the WirelessHART standard in detail, where functionality and structure of each layer are presented. A WirelessHART network consists of several devices performing different tasks, each introduced in turn. After the WirelessHART protocol we present the hardware and software used to build a test network for evaluating our implementation. The aim of the project changed as the devices used were found unsuitable and out-of-date. We changed the direction of the report to focus on the Network Manager and less on the nodes as they were already thoroughly researched. The implementation part presents a total restructuring of the Gateway, where communication between the different layers are achieved through interfaces. The Gateway correctly propagates advertise packets, initiating a complete join sequence between a node and the Network Manager. The Network Manager generates routes using a graph routing scheme. These routes are used by devices to transmit packets through the network.Security mechanisms and packet construction are implemented according to the standard, providing a packet structure according to the layered approach. We conclude the report with an evaluation of the project, comparing the results to our project goals.