This was my first textbook in college for my intelligence courses. It's a good book. It's dry but remember it isn't supposed to be a novel. There were some concepts a bit to advanced for me. Once he gets into the math of it it became super slow reading for me. But it's very informative.
Clauser's Introduction has been published since the 1970's, providing assistance on how to perform research for an intelligence-gathering community, qualities sought in intelligence analysts, and helpful methods toward employment in an intelligence environment.