Dark matter not only forms an invisible cosmic scaffolding within which galaxies form, its distribution in the universe also contains a wealth of information about fundamental physics. Measurements of gravitational lensing in the cosmic microwave background (CMB) allow this matter distribution to be directly seen and mapped. In my talk, I will discuss current and future work in this new, rapidly advancing field. In particular, I will show new measurements of CMB lensing with the ACTPol experiment and discuss how upcoming ultra-high-precision studies of the lensing signal will probe the properties of neutrinos and dark energy. Lensing is not only a signal, however, but also a source of noise that limits how much we can learn about the very early universe. With illustrations from recent work, I will explain why delensing - removing the lensing effect to reveal the primordial sky - is crucial for the future of CMB cosmology.