Latent thermal energy storage is able to store a large amount of thermal energy by making use of the heat of fusion required for the physical state transformation of phase change materials (PCMs). It has significant implications in harnessing renewable energies and adjusting electricity peak load. This paper reviews PCM latent heat storage systems for heating and cooling applications; both early stage developments and latest discoveries are discussed. The principles backed up these systems are investigated; pros and cons of different types of phase change materials as well as the systems utilizing these materials are compared. PCM incorporation in building structures is emphasized as it represents the recent development in the subject of latent thermal energy storage. The compatibility of PCMs with different building materials is discussed, and the energy saving potential is predicted. In addition, a couple of novel cooling systems employing PCM latent thermal storage are introduced at the end.