Over the next decade, significant progress must be made in research on computer architectures that enable unprecedented improvements in the efficiency of large-scale computing systems, particularly to support applications that require exascale algorithmic performance. Here, we review the performance requirements for both high-performance computing systems and data centers, and show that it will be critical to exploit photonic devices for interconnect applications to meet these expectations. In the long term, CMOS-compatible fabrication technologies promise a “Moore's Law for photonics” that could completely change the economics of integrated optics and high-performance computing for defense, security, scientific, and consumer applications.