Lawrence Livermore National Laboratory (LLNL) has a long history of leadership in large-scale computing. Our next platform, Sierra, a heterogeneous system that will be sited as part of a Collaboration between Oak Ridge, Argonne and Lawrence Livermore National Laboratories (CORAL) and delivered through a partnership with IBM, NVIDIA and Mellanox, will continue that tradition. That partnership has reached a key milestone that has begun the siting of Sierra as well as the Summit System at ORNL. This talk will provide a detailed look at the design of Sierra. It will compare and contrast Sierra to Summit, explaining the motivation for the design choices of each system. It will also preview some early uses of Sierra that target its technical opportunities and the challenges that accompany them.