Molecular solar thermal (MOST) systems have raised great attention in solar energy storage and release, which can generate high-energy metastable isomers upon harvesting photon energy, and release the stored energy as heat on demand through reversible photoisomerization of molecular photo-switches. Various azobenzene-based MOST systems have been fabricated by several strategies including molecular engineering and template self-assembly, among which azobenzene-containing polymers (azopolymers) are recognized as the most hopeful materials for the development of MOST systems because of the benefits of their ease of forming uniform and flat films of controlled thickness. This chapter first introduces the advantages of azopolymer-based MOST systems. Then, recent research advances in azopolymers for solar energy storage and release are described including azobenzene compound/polymer composites, linear azopolymers, and dendrimer azopolymers. Finally, several azopolymer-based MOST functional devices are summarized, and future research directions and application prospects are proposed.