National Alliance on Mental Illness: www.nami.org
Provides a brief overview of principles of Cognitive-Behavioral Therapy (CBT) and how it applies to various presenting problems.
National Association of Cognitive-Behavioral Therapist: www.nacbt.org
The NACBT is the leading organization dedicated exclusively to supporting, promoting, teaching, and developing CBT and those who practice it. The link above provides a detailed explanation of what CBT its fundamental theories.