The availability of low cost, low power, and miniature embedded processors, radios, and sensors, integrated on a single chip, is leading to the use of wireless communications and computing for interacting with the physical world in many civilian and military applications. The resulting systems, called Wireless Sensor Networks (WSN). The advances in the integration of complex wireless integrated products and the increase in performance and functionality of the design tools, the requirements and properties of a single device (sensor node) are well understood. Yet it is not simple and straightforward to implement WSN concepts into a functional prototype system or even a commercial product. This tutorial will address the key factors in WSN design. The capabilities of the current WSNs will be examined. The new security scenarios for WSN will be illustrated. Different localization techniques in WSN will be discussed and compared. Future trends in WSN research will be introduced.