Measurements of gravitational lensing in the cosmic microwave background (CMB) allow the dark matter distribution to be mapped out to uniquely high redshifts. After giving an overview of current and upcoming CMB lensing measurements with the Atacama Cosmology Telescope and beyond, I will focus on two new ways of using CMB lensing, in combination with galaxy surveys, to constrain the early universe. First, I will explore how CMB lensing and galaxy surveys could provide insights into current discrepancies in measurements of the Hubble constant. Second, I will explain why new approaches to de-lensing – removing the lensing effect to reveal the primordial polarization sky – will be important for probing the early universe with the Simons Observatory CMB experiment.