The use of sandwich-type construction is very prevalent in the aerospace industry as can be seen from their use in aircraft engines, the fuselage, the floor, side panels, overhead bins, and the ceiling. Other applications include their use in naval ship bulkheads, deck houses, aircraft hangers, locomotive cabs, buses, satellites, automobiles, etc. All of these applications create a need to understand the structural performance of these structures under complex loading conditions. This chapter begins with a brief overview of sandwich structures discussing the types of sandwich structures, the components of sandwich structures, their applications, properties of the structure, manufacturing methods, and a detailed historical presentation followed by a detailed comprehensive discussion of the failure modes of sandwich structures with associated figures. Finally, a discussion of the future of sandwich structures is discussed emphasizing that challenges needed to be overcome. For the benefit of the reader the contents of the monograph are discussed in its entirety.