To support the current trends in cloud, Internet of Things, 5G, etc., massive amounts of data need to be processed and stored with very different performance requirements in terms of capacity, granularity, delay, etc. These requirements drive the need for both mega-size data centers (DCs) and distributed micro DCs interconnected with high-speed communication links. This special issue focuses on the key role of optical networking in meeting these requirements through high-capacity, energy-efficient, and flexible connectivity, and presents recent advancements in DC architectures, network solutions, and optical technologies needed to interconnect computing and storage resources within and between DCs.