Abstract : In this chapter, the behavior of unsaturated granular materials will be analyzed by focusing mainly on capillary cohesion. Two formulations of the capillary cohesion law will be presented in section 9.2. The first one was proposed by Soulié [SOU 05, SOU 06b]. It expresses the capillary force as a function of the interparticle distance and the volume of the liquid bond between two particles of different sizes. This formu- lation has been validated by an experimental study at the scale of the liquid bond. The second formulation proposed later by Richefeu et al. [RIC 06b, RIC 07] is an analyti- cal expression based on physical considerations. A 3D molecular dynamics code was developed in which the capillary interaction law for the simulation of wet granular ma- terials was implemented [RIC 05]. The simulations of direct shear [RIC 05, RIC 06a] and simple compression [SOU 05, RIC 05, SOU 06a] tests are presented in sections 9.3 and 9.4, respectively. The focus in both cases will be on the influence of capillary cohesion on the macroscopic mechanical behavior and failure of wet granular media.