Wireless sensing systems are increasingly used both in more conventional applications and mainly in situations requiring some of their specific capabilities. Most measuring systems advising or requiring a huge number of sensors and sensing nodes that cover a more or less large área are possible to implement only if organized as centrally managed wireless networks of stand-alone nodes. Each node is provided with processing capabilities and incorporates the hardware and software required for data acquisition, data processing and data transmission to the network central unit. Such measuring systems are labelled wireless sensor networks (WSNs) and in the article the authors give an overview of the state of the art, the problems to overcome and the future trends of WSNs.