The use of fibre-reinforced plastics (FRPs) in sandwich structures increased for various industrial applications thanks to their strength-to-weight ratio which provides designers with advanced options for modern structures. FRP Sandwich Structures (FRPSS) are often used in aerospace, biomedical, defence, and marine products, where their high structural performance is required to sustain complex in-service loads and withstand varying environmental conditions. Progressive degradation of FRPSS under such circumstances has been a subject of interest for researchers owing to safety requirements for products with FRP. This paper reviews the state-of-the-art of the mechanical behaviour of FRPSS subjected to various loading regimes. It highlights the variation in structural performance, viscoelastic properties, damage resistance, and sequence of environmental degradation of FRPSS. Numerical methods and damage algorithms used to predict failures are also presented to provide sufficient knowledge for the design of FRPSS. This review contributes to further research on characterizing the properties of FRPSS under quasi-static and dynamic loading conditions.