Abstract: Rubble pile asteroids have been frequently characterized as being cohesionless, self-gravitating aggregates of boulders and grains. This picture has motivated many geophysical theories for how these bodies evolve in the solar system, and what assumptions can be made concerning their evolution and exploration. However, recent astronomical observations of asteroid 1950DA and active asteroid P/2013 R3 have provided evidence that this picture is incomplete, and indeed that rubble pile asteroids can exhibit a degree of cohesion between their components. The net effect of even small amounts of cohesion has significant implications for the evolution of small asteroids in the main belt and in the NEA population, and will be reviewed. A recent theory by Sanchez and Scheeres provides one hypothesis for how such cohesive strength could exist in gravitationally attracting aggregates — through weak van der Waals attractive forces between the finest grains in a rubble pile. This theory has several additional implications for the asteroid environment that have specific predictions that can be probed with both ground-based observations and with spacecraft rendezvous missions such as Hayabusa II and OSIRIS-REx.