Sensor Nodes in Military Applications always suffer constraints over energy due to their small size & when we want to apply hard security algorithms we need to consider the energy factors as well because security and energy always behave in inverse proportions. In this book, we have presented a security model independent of energy (SMIE) for Wireless Sensor Networks designed with actual availability of never lasting energy within the network rather than any assumption. This model provides ample amount of energy supplied wirelessly to the Base Station as well as to the sensor nodes in the deployment area, besides a new key management technique that overcomes the drawback of all existing strong keying techniques is proposed at a very reasonable cost. The solution is designed keeping in mind the deployment of sensor nodes in isolated environment as well as in military applications, where human interference is low but surveillance is at high priority. The book considers Base Station as flying object like UAV and provides solution to the challenges which it can face in such type of scenario. The book will open a number of new research aspects in the field of Wireless Sensor Networks.