Wet Granular Matter A Truly Complex Fluid

1. Introduction. 1.1. The significance of wet granular matter. 1.2. Energy scales. 1.3. Typical questions to be asked. 1.4. How we shall proceed -- 2. Grains and granular fluids. 2.1. Grains. 2.2. Granular fluids. 2.3. Conclusions -- 3. Wetting. 3.1. Planar substrates. 3.2. Rough substrates. 3.3. Conclusions -- 4. Capillary forces. 4.1. Capillary bridge between flat walls. 4.2. Capillary bridge between spherical bodies. 4.3. Capillary bridge between irregular grains. 4.4. Force networks. 4.5. Conclusions -- 5. Wet granular gases. 5.1. Dynamical aspects of capillary bridges. 5.2. Free cooling and clustering. 5.3. Liquid-gas coexistence. 5.4. Collective phenomena far from thermal equilibrium. 5.5. Conclusions -- 6. Wet granular piles. 6.1. Geometrical aspects of granular piles. 6.2. Regimes of wetness. 6.3. Mechanical properties of wet granular piles. 6.4. Phase transitions in wet granular piles. 6.5. Conclusions -- 7. Special topics. 7.1. The physics of sand castles. 7.2. Immiscible granular suspensions. 7.3. Quicksand and quickclay