This book considers distributed capability systems as a potential solution to securing data in cloud environments. The U.S. Navy, Intelligence Community and Department of Defense have begun a significant investment to leverage scalable, distributed cloud-based solutions for information sharing. We believe capability systems suggest a promising direction for new platforms, a bold approach drawing directly from mature ideas first explored in the 60s and 70s. We survey the properties and limits of existing distributed capability file systems, as a step toward understanding how capability-based designs might serve cloud-scale systems. We highlight some lessons learned in our observations and find that, while no existing capability-based distributed file system demonstrates all of the desirable security traits observed of smaller-scale capability systems, it should be possible to define and create one that does, using capabilities carefully designed to obey a set of known properties.