Part of the 3-D incompressible Navier-Stokes equations may be lie in the physical quantity: helicity which is rather mysterious in itself. It is well-known that for 3-D incompressible Euler equations, the global integral of helicity is conserved. However, the helicity density does not have a fixed sign, and hence hard to use in analysis. In a recent joint work with Zhen Lei and Yi Zhou, we explored a structure of helicity, and from it, we derived an energy law for regular solutions of the 3-D incompressible Navier-Stokes Equations. Unlike the classical Leray-Hopf energy (which is only known one), which is supercritical with respect to natural scalings, this new energy is actually critical with respect to scalings. From this one can derive some global existence of smooth solutions.