The purposes, authorities, and instruments of congressional oversight are described in detail in a newly-expanded Congressional Oversight Manual (pdf) prepared by the Congressional Research Service.
“Congressional oversight and investigations can often, though not always, become adversarial,” the CRS Manual observes. “This is especially true when the entity being targeted, whether a private individual, corporation, or executive branch agency, has information Congress believes is necessary to its inquiry but refuses to disclose. In those situations the targeted entity may attempt to use several methods of avoiding disclosure. A commonly used tactic to avoid disclosure is to assert that the information cannot be disclosed due to a specific law, rule, or executive decision. Another common tactic is to assert that the information itself is of such a sensitive nature that Congress is not among those entities entitled or authorized to have the information.”
The Manual proceeds to scrutinize the validity of such tactics, and discusses the options available to Congress to compel disclosure. A copy was obtained by Secrecy News. See Congressional Oversight Manual, Congressional Research Service, 168 pages, January 6, 2011.
Other noteworthy new CRS reports include the following (both pdf).
Ricin: Technical Background and Potential Role in Terrorism, December 21, 2010.