In this paper two methods to design dual band and high efficiency power amplifiers using Composite Right/Left Hand (CRLH) and Extended Composite Right/Left Hand (ECRLH) transmission lines are described. The CRLH and ECRLH transmission lines, design procedure and design equations are presented. As example of application the design of an CE class amplifier appears. The non-linear phase response of a CRLH and ECRLH transmission line has been utilized to design arbitrary dual-band amplifiers. The simulations results are presented at the end of the paper, demonstrating the validity of the use of this type of lines in the design of amplifiers