Testimony presented to the Senate Select Committee on Intelligence by Kim Cragin of RAND on 12 Jun 07:

Understanding Terrorist Ideology
Over the past twelve years, during the course of my research on terrorism and insurgency, I have explored the topic of terrorist ideology as it relates to what motivates individuals to become terrorists, as well as what influences communities to sympathize with terrorist groups. This research can be found in a number of RAND publications, including Terrorism and Development, and more recently, Dissuading Terror.

Both issues – individual motivations and community support – are important to understanding the challenges that extremist ideologies pose to US national security. For example, potential exists for terrorist groups to use various ideological arguments to persuade individuals to ‘pick up a gun’ or become terrorists themselves. Potential also exists for terrorist groups to use ideological arguments to garner financial or other support from local communities. And yet, despite this potential, it remains uncertain to what degree ideology actually influences individual motivations or community support. Indeed, our research suggests that the impact of ideology tends to vary country by country, community by community and often individual by individual....
The wasn't the only testimony presented; unfortunately the hearing transcripts aren't up on the committee website. If I find the others I'll post'em on this thread.