 If a court decides that an opinion should be published, the opinion may be included in a volume from a series of books called law reports (or reporters in the United States).Published opinions of courts are also collectively referred to as case law, and constitute in the common law legal systems one of the major sources of law.Not every case decided by a higher court results in the publication of an opinion; in fact many cases do not, since an opinion is often published only when the law is being interpreted in a novel way, or the case is a high-profile matter of general public interest and the court wishes to make the details of its ruling public.