For many decades, the staff of the Joint Committee on Taxation of the U.S. Congress has prepared a summary, at or near the end of a congressional session, of significant tax legislation enacted during that session. This summary, officially known as a “General Explanation” and more commonly called the “Blue Book” because it is enclosed within blue covers.  Recently, the Supreme Court of the United States had occasion to consider just what official credence should be accorded to Blue Books.