The increase in usage of composite structures has raised the necessity for evaluating in-service performance. Due to complexity in design, high operational loads, and longer lifetime, composite structures are prone to unpredicted failures. Current-day nondestructive evaluation techniques, such as ultrasonic testing, acoustic emission, eddy current method, radiography, thermography, etc., are primarily meant for metallic materials and not always very effective for composites because of inherent micromechanical complexities. Structural health monitoring (SHM) is an important method that can be used to monitor the health of composite structures and has been around for more than two decades. It is mostly confined to laboratories and industries to examine the defects associated with composite material, especially for aerospace and civil application. This chapter on maintenance and monitoring of composites explains the advantages of implementation of SHM for composite structures and the limitations of present-day nondestructive testing (NDT) methods based on numerous amounts of publications and research carried out by researchers. In this chapter a detailed review has been presented for SHM for polymer composites and a comparison has been made between SHM and NDT. Also, various challenges for SHM along with feasible and emerging SHM techniques that include piezoelectric, acoustic-ultrasonic, acoustic emission, and electrical mechanical impedance methods have been explained in detail. Composites are anisotropic in nature, so their properties vary with applied changes, which is the main source of problems in monitoring the health of a structure made of composites as the damage is difficult to predict. Thus it becomes important to determine the accurate position and the speed of the damage propagation including submicron-sized cracks in the composites. © 2019 Elsevier Ltd. All rights reserved.