Online apps that matter are geo-distributed, because they serve millions of users around the world. Geo-distribution is important for latency, availability, and increasingly also for efficiency. Due to rapid growth in the volume of demand served, large numbers of geo-distributed data centers today can benefit from the same multi-megawatt economies of scale that were initially limited to a few centralized ones. As a result, modern cloud infrastructures are already highly geo-distributed. Trends such as our increasing reliance on online services, and the growth in mobile device usage that has converted many client based applications into cloud services, indicate that data center infrastructures will be even more geo-distributed in the future. This session discusses challenges in designing a geo-distributed data center infrastructure and developing software applications for it.