Wireless sensor networks are being employed in a variety applications ra- ing from medical to military, and from home to industry. The principle aim of this book is to provide a reference tool for the increasing number of scientists who depend upon sensor networks in some way. The book is organized into several sections, each including chapters exploring a specific topic. Wireless sensor networks are attracting great attention and there are many research topics yet to be studied. In this book, the topics covered include n- work design and modelling, network management, data management, security and applications. The articles presented in the book are expository, but of a scholarly nature, including the appropriate history background, a review of the state-of-the-art thinking relative to the topic, as well as a discussion of unsolved problems that are of special interest. The target readers of this book include the researchers in computer s- ence, computer engineering, and applied mathematics, as well as students in these subjects. Specialists as well as general readers will find the articles st- ulating and helpful. Book Organization The book is organized into five sections. Section I introduces the design and modelling of sensor networks. Chapter 1, by Iyer, Kulkarni, Mhatre, and Rosenberg, presents a taxonomy of wireless sensor networks, based on their application level objectives, tra–c characteristics and data delivery requi- ments. Popa and Lewis in Chapter 2 describe some algorithms for systematic exploration of unknown environments using a mobile wireless sensor network.