Wellbore cement integrity is paramount to safe, successful oil and natural gas drilling. Cement acts as the primary barrier between the wellbore and the environment. An unstable cement can compromise wellbore control, and research indicates that poor cement integrity is a primary factor contributing to loss of zonal isolation in oil and gas reserves. Although cementing designs and placement practices are well established in many operational environments, the extreme subsurface conditions found in deepwater oil and unconventional natural gas reservoirs pose new challenges to achieving reliable cement jobs. With resource recovery in these types of reservoirs on the rise, the National Energy Technology Laboratory (NETL) and its partners in the NETLRegional University Alliance (NETL-RUA) are examining the performance and integrity of key wellbore barrier materials for which data in extreme environments are limited. One of those materials is wellbore cement. Our researchers are working to understand how various cement mixes perform, with emphasis on potential failure pathways and remediation technologies. This work builds on long-standing research conducted by our organizations to understand and develop technologies for drilling systems associated with onshore oil and natural gas development. It also builds on our work in geologic CO2 storage, which is looking at the effect of stored CO2, acid gas, and brine solutions on the integrity of cements at high pressure and temperature. As the breadth and scope of cementing evolves and industry drills toward deeper, more complex targets, the initial and long-term integrity of cement barriers, and the protocols for placing them, are critical to safe, productive hydrocarbon recovery.