Restatements of the Law are attempts to restate various areas of American common law in a clear and organized manner. Restatements are valuable secondary sources because in addition to their restating of the provisions of the common law, they also contain examples illustrating their provisions and notes explaining the views of the committee members on each provision. Also, they are regarded as highly persuasive by courts, which often look to them when dealing with an area of law that has not been developed in a particular court's jurisdiction.
The Restatements are a project of the American Law Institute (ALI). The ALI has had several cycles of restatement projects. The first cycle begain in 1923; the second in 1952; and the third, still on-going, in 1987. Restatements are referred to according to the cycle in which they were written, e.g. the Restatement, Third, The Law Governing Lawyers (this Restatement originated in the third cycle; there was no predecessor Restatement, Second, or Restatement of the Law).
The ALI has also produced a number of projects referred to as Principles of the Law. These Principles are written in areas where the law is predominantly based on statutes, not the common law. They are addressed to courts, legislatures, and parties; they restate how the law has developed in certain areas, they suggest how the law ought to develop in the future, and they recommend how parties ought to act.
In some areas, the ALI has not been able to formulate Restatements because the law is not settled or the states differ too much. For criminal law, the ALI produced the Model Penal Code, a statutory proposal that stated what it thought legislatures should adopt as the law. Suspended ALI projects can be found in the American Law Institute Library on Hein Online (see the tab for "Electronic Resources"). Information on model acts can be found in the law library's research guide on Model Codes.
Information on citing the Restatements can be found in the Bluebook (19th ed. 2010) at R12.9.5 and B5.1.3.