Substantial progress has been achieved since 1999 in understanding the phenomenon of terrorism financing and in articulating and implementing the measures necessary to address it. Terrorism financing incorporates the distinct activities of fund-raising, storing and concealing funds, using funds to sustain terrorist organizations and infrastructure, and transferring funds to support or carry out specific terrorist attacks.  Funds used to support terrorism may be generated through legal or illegal means, and legitimate humanitarian or business organizations may be used unwittingly or knowingly as a channel for financial or other logistical support to terrorism. Financial transactions can yield valuable intelligence that may be unavailable from other sources. Yet, detecting illicit financial activity, including terrorism financing, is difficult in the formal financial system and even more difficult outside of it.