In this book we propose an energy-efficient secure routing for wireless networks based on symmetric key cryptography. The proposed crypto system is session based and the session key is changed after the expire of each session. We divide the network into number of clusters and select a cluster head within each cluster. Communication between sensor and the sink takes place at the three levels; sensor cluster-head sink. Encryption of the sensed data is transmitted to the cluster head, which aggregated the data received from the sensor nodes of its cluster before forwarding to the next cluster head on the path or to the sink . Sensors do not participate in the routing scheme; their energy is conserved at each sensor node.