A legal opinion is a document written by a judge which accompanies a legal decision. The opinion explains how the judge arrived at a ruling, and may offer additional thoughts and commentary. In the event that the opinion is published, it becomes part of case law in nations with a common law system, which means that it can be utilized in future legal cases. For this reason, judges craft legal opinions very carefully.
Usually, a legal opinion is published if a case is of special interest, or if there is something unusual about the ruling. For example, if a judge sets a precedent, challenges an existing law, or provides a novel interpretation of the law, the legal opinion would be published. Likewise, legal opinions from high courts, in which judges are called upon to interpret very complex legal challenges, are usually published.
If multiple judges provided a ruling, one judge will usually write the majority opinion, explaining the position of the majority in the case. Another judge may write a dissenting opinion, explaining why he or she disagreed with the majority. Both opinions can enter case law, and can provide valuable information about interpretation of the law, and how to pursue similar cases in the future. In addition, a judge can write a concurring opinion, adding thoughts and commentary to the majority opinion.
The law is continuously evolving, and legal opinions are an important way of shaping the law. In some cases, issues are actually brought to court with the goal of challenging the law, rather than winning a particular outcome. Cases brought before the high court are usually carefully chosen and formulated for this very reason, with justices being well aware that their opinions in such cases can have long-lasting repercussions.
Legal opinions can be quite elegant and sometimes eloquent as well. They are not necessarily stiff and dry, although they sometimes are, and some judges even throw in humor or asides. Some court reporters make a beat out of ferreting through legal opinions for humorous asides. Some judges have taken this to a high level: in Pennsylvania v. Dunlap, a case heard before the United States Supreme Court, Justice Roberts opened his dissenting opinion with an outlining of the case that read like something from a detective novel.
People sometimes use the term "legal opinion" to refer to advice or opinion offered by a legal adviser, rather than to a legal opinion issued by a judge.