Flexible antennas have become popular in recent years due to their wide range of applications in different sectors and their ability to withstand variable operating conditions. Designing and fabricating a flexible antenna that can function effectively under various operating situations without compromising performance or design requirements is still a challenge. For this reason, cutting-edge design techniques and materials are needed to get around these constraints. Metamaterials’ use in flexible and wearable antennas has received recent attention because of their various advantages. Metamaterial structures can be loaded into the design to increase the performance of the flexible antennas with minimum effect on the human body when they are implemented for wearable applications. This chapter presents a review of the key progress of the use of metamaterial in flexible and wearable antennas with their advantages and challenges.