This chapter reviews the aerospace applications and challenges of deployable composite structures. Since the 1970s, composite materials have replaced metals in deployable structures, such as glass fiber composite masts on Voyager. Deployable composite hinges are used in space telescopes, while booms (lenticular, bipod) feature in solar sails and deorbit sails (e.g., China’s Taurus deorbit sail, Pujiang-2 film antenna). Reflectors like taco-shaped models have operated on Mobile Sat-1 and TDRSS. Future challenges include improving folding behavior modeling, enhancing extreme environment adaptability, and advancing multi-objective optimization, requiring breakthroughs in theoretical models, material properties, and auxiliary device design to boost reliability and functionality in space applications.