Wireless sensor networks have a wide range of applications in the field of Civil, Industrial, Health, Agriculture, Home Automation, Military and other areas. In a clustered network, the nodes are grouped into clusters each having a co-ordinator called cluster head (CH) responsible for collecting the data from all the nodes present in each cluster. The cluster heads are selected based on single or multiple criteria to enhance the overall lifetime of the network. This leads to effective management and energy efficient data transfer between the nodes and the sink. Based on the design constraints, this book presents various energy-efficient clustering algorithms that provide large benefits to the applications. These algorithms are designed to meet specific goals such as higher network lifetime of the network, lower average energy dissipation, higher number of data packets received and better stability region. The simulation results depict that all the algorithms are more effective in prolonging the network lifetime than other existing protocols.