<p>Smart fibers and textiles have attracted considerable interest for application in wearable devices because of their advantages of being human-friendly, lightweight, flexible, and comfortable. In addition, they are considered to have potential applications in health monitoring, energy management, and human-machine interaction systems. Polymers and polymer fibers, with excellent mechanical strength, wrinkle resistance, and heat resistance, are widely used to fabricate smart fibers and textiles. Herein, a comprehensive overview of polymer-based fibers and textiles is provided. First, we review the design principles of various polymer-based smart textiles, including textile-based sensors, energy capture and storage textiles, and computation and display textiles. Next, materials used for preparing polymer-based smart fibers, such as metals, carbon-based materials, and natural and synthetic polymers, particularly conductive polymers, are summarized. In addition, this review summarizes key technologies used for preparing smart fibers and the conventional structures of smart textiles. Furthermore, the applications of smart textiles in personal health monitoring, thermal management, energy capture and storage, and computation and displays are discussed. Finally, the current challenges, limitations, and future trends of smart fibers and textiles are discussed.</p>