Low energy trajectories will be increasingly used in future space missions, due to the possibility of large savings in fuel cost (as compared to classical approaches) by using natural pathways arising from the presence of a third body. Our recent work provides a rigorous foundation for understanding and utilizing low energy passageways by applying some techniques from dynamical systems theory to systems of N bodies considered three at a time. The boundaries of these passageways are realized geometrically as invariant manifolds attached to equilibrium points and periodic orbits in interlinked three body problems. The emerging picture is of tube-like structures forming an interplanetary transport network which will facilitate the exploration of the Moon, the asteroids, and the outer solar system, including future missions to assess the possibility of life on Jupiter's icy moons. We summarize these ideas, including their relationship to other problems in dynamics and control, and discuss future directions.