Layered fiber-reinforced composite structures are susceptible to crack initiation and growth in the resin-rich layer between plies. Delamination represents one of the most prevalent life-limiting failure modes in laminated composite structures. Interlaminar fracture mechanics represents one approach to assess the damage tolerance of composite structures. This paper is organized into two major sections. The first sections introduces interlaminar fracture mechanics and test methods that have been developed to characterize the Mode I, II and III interlaminar fracture toughness of composite laminates. In the second section, the role of interlaminar fracture mechanics in assessing damage tolerance of composite structures is defined through the following case studies: residual compression after impact strength, instability related delamination growth in compressively loaded laminates and delamination growth in composite laminates with discontinuous internal plies.