Book excerpt: Polymers are one of the most versatile and important materials used for capsule preparation despite various others available. Suitably formulated capsules can securely protect ingredients, deliver them to targeted sites, and release them expeditiously, improving functions and minimizing adverse effects. New polymers are constantly being explored to develop more efficient capsules as they are routinely used in pharmaceuticals, consumer healthcare products, nutrients, and food. This book focuses on the current state of the art of polymer-based capsules and delivery systems. It describes the formulation processes of capsules developed from redox-responsive polymers and polymer-functionalized carbon nanotubes, in addition to shedding light on coacervation of polymers for encapsulation. It reviews different active ingredients that can be used with polymer capsules in various products, encapsulation of essential oils using such capsules, and development of polymer capsules of cells and bacteriophages.