Here an advanced tutorial on power control issues in all generations of cellular system has been presented. Power control represents a key degree of freedom in design of cellular system, offering substantial benefits for efficient and fair of operation of the system, especially in energy efficient designs. It also supports several functionalities including QoS, bit error rate optimization and energy efficient designs in all stages of cellular system. Taking energy efficiency into account, performance of different power control algorithms have been analyzed as a function of transmitted power with some interesting results.