Damage accumulation and rupture of network materials are discussed in this chapter. The chapter is divided into two parts addressing the rupture of networks without and with pre-existing defects. The relation between the network structure and the strength and ductility of materials without pre-existing cracks is defined, and examples from gels, cellulose networks, and nonwovens are provided. The effect of the fiber tortuosity, fiber aspect ratio, fiber preferential alignment, and the variability of fiber and crosslink properties on network strength is discussed. As in other materials, the size effect on strength is important in Network materials and a section is dedicated to statistical aspects of the strength. Failure under multiaxial loading conditions is compared with failure in uniaxial tension. The second part of the chapter presents an analysis of the propagation of cracks in networks. Pronounced notch insensitivity is observed in many materials and numerous examples are presented. Special attention is given to toughness and guidelines are provided to assist the toughening of quasi-brittle Network materials. A subsection is dedicated to the strength, toughness, and fatigue resistance of elastomers and gels.