For the purposes of the workshop, the “dark web” is defined as “the hyper-linked services on the dark net that can only be accessed using the Onion Router (Tor) protocol or other equivalent technologies.” Some online criminal activity relies on the “dark net,” a portion of the Internet that uses encryption and anonymizing technologies that are intentionally designed to frustrate tracking efforts. On the dark web, the process of collecting crime-related data and turning them into evidence can be difficult. Because of the increasing number of illicit transactions, the dark web is now drawing the attention of law enforcement agencies. The workshop that is the focus of this report was attended by practitioners from federal, state, and local law enforcement, as well as researchers with expertise in cyber crime. Panelists’ discussions addressed the following topics: general challenges, including globalization and training; technical challenges, including anonymity and access, suspect identification, and resource allocations; and legal challenges, including the multijurisdictional nature of these crime types. Panel members identified 40 problems and 46 potential solutions that they believed could benefit from additional investment in research and development. Taken together, the high-priority needs identified during the workshop present a pathway for preparing law enforcement personnel at all levels to better address the challenge posed by cyber crime. Recommendations pertain to training, particularly in what the dark web is and how criminals leverage it; information-sharing and cooperation across agencies; and research into updating laws related to inspecting packages transmitted through the U.S. mail and similar services.