In principle, a network can transfer data at nearly the speed of light. Today’s Internet, however, is much slower: our measurements show that latencies are typically more than one, and often more than two orders of magnitude larger than the lower bound implied by the speed of light. Closing this gap would not only add value to today’s Internet applications, but might also open the door to exciting new applications. Thus, we propose a grand challenge for the networking research community: building a speed-of-light Internet. To help inform research towards this goal, we investigate, through large-scale measurements, the causes of latency inflation in the Internet across the network stack. Our analysis reveals an under-explored problem: the Internet’s infrastructural inefficiencies. We find that while protocol overheads, which have dominated the community’s attention, are indeed important, reducing latency inflation at the lowest layers will be critical for building a speed-of-light Internet. In fact, eliminating this infrastructural latency inflation, without any other changes in the protocol stack, could speed up small object fetches by more than a factor of three.