In Funding Evil, a valuable contribution to the study of how money eventually appears in the pockets of terrorists, Ehrenfeld focuses on the shadowy world of the global terrorist financing network in all its intricacy and complication. She does so through an extensive study of the mechanisms used to collect and launder millions of dollars. Using informative, timely cases, she illustrates the phenomenon of fraudulent Islamic charitable fronts and unregulated hawala (debt transfer) networks, with particular emphasis on the role that illegal narcotics plays in both. While Al-Qaeda and its affiliates are a major topic of inquiry, there is also extensive discussion of the parallel financial networks of other militant movements—including Hamas and Hizbullah—to which cash continues to flow, despite the substantial progress made by intelligence and law enforcement since September 11.

Ehrenfeld makes specific and useful suggestions for "tools to fight terrorist financing"—ideas to be taken seriously by contemporary Western policymakers. In particular, she recognizes that resolving corruption and cronyism in the developing world is key to eliminating the underlying problem of international terrorist financing.

Unfortunately, factual errors mar the book, perhaps a consequence of a regrettable lack of primary sources for many of the case studies. Too many sources are newspaper articles from unreliable publishers. For example, Ehrenfeld labels criminal suspects involved in a terrorist-linked scheme to trade Stinger missiles for drugs as "members" or "operatives" of Al-Qaeda without providing the evidence for this assertion. She also quotes an anonymous Western intelligence source stating that former University of South Florida professor Sami al-Arian—accused of helping fundraise and propagandize on behalf of Palestinian Islamic Jihad—was likewise "one of Al-Qaeda's most important U.S. operatives." These accusations require additional facts for independent corroboration.