If you are unclear about what Uniform Laws are see the LII "Uniform Laws" page.
In the American federal system, both the federal government and the individual states have the power to pass statutes or laws. (Local governments like counties and cities can as well but have more limited power generally seen as derived from their state.) Both are subject to constitutional limitations. Some topics are largely covered by federal legislation, some are handled almost exclusively by the states, and many are the subject of both state and federal law.
As interstate business and individual movement have increased in the U.S. the felt need for greater uniformity of law on particular subjects has grown. One response to such a need is enactment of a federal law on the subject (e.g., the federal Securities Act of 1933). Another approach known by the name "Uniform State Laws" seeks adoption of identical or similar laws by all the states. It dates back to the late nineteenth century.
A non-governmental body, the National Conference of Commissioners on Uniform State Laws (NCUSL) was formed in 1892 upon the recommendation of the American Bar Association for the purpose of promoting "uniformity in state laws on all subjects where uniformity is deemed desirable and practicable." Made up of lawyers chosen by the states, the Conference oversees the preparation of proposed laws, "Uniform Laws" which the states are encouraged to adopt. For over a century this process, carried out through committees that prepare successive drafts for review and ultimate approval by the full Conference has continued to function. To date, the Commissioners have approved more than two hundred uniform laws, of which more than 100 have been adopted by at least one state. A few have been widely adopted and have, as a consequence, approached the hoped for uniform national law on their subject.
The phrase "Uniform Laws" can be misleading. Upon approval by the National Conference a Uniform Law is not law anywhere in the United States. It is simply a legislative proposal addressed to fifty state legislatures. During the history of the Conference, roughly half its proposals have not been adopted by a single state. (Examples include the Uniform Construction Lien Act (1987), the Uniform Franchise and Business Opportunities Act (1987), the Uniform Putative and Unknown Fathers Act (1988).) In addition, most of those that have enjoyed reasonable success have fallen way short of the goal of adoption by all or even a majority of the states. Furthermore, the versions of the "Uniform Laws" passed by the states are rarely uniform. Variations occur at the outset since prior law or other special local conditions lead states to make changes; rarely do states adopt Uniform Laws verbatim. A second source of variance is the Conference itself. Having adopted a successful Uniform Law, the Commissioners are prompted, just as true legislators are, to revised it from time to time in the light of changing conditions and policies. This results in multiple versions of some Uniform Laws, and unless and until the states that adopted an earlier version enact the Commissioners' revisions in multiple versions in effect in the states. There are, for example, at least two versions of the Uniform Probate Code in force in the states, the original code and 1989-1990 revisions which some states have not adopted and others have adopted only in part. (See the LII's Uniform Probate Code Locator page). In short, uniformity has proven an illusive goal.
The greatest successes of the "Uniform Law" approach have been in the field of commercial and business law. Beginning with the Commissioners first product, the separate Uniform Negotiable Instruments Law (at one time in effect in all the states) and Uniform Sales Act (also widely adopted), the Conference, working together with the American Law Institute, later produced the Uniform Commercial Code (now in effect in some version in nearly all U.S. jurisdictions -- see the LII's Uniform Commercial Code Locator page).
While uniformity was the original aim of the Uniform Law process overseen by NCUSL, in time law revision or reform became a significant purpose as well. Topics for legislation where state to state variance did not create a serious problem for the conduct of business or interstate mobility but where state laws were judged by legal experts as being in need of reform have been the subject of Uniform Laws. To the extent particular acts are justified by this broader aim, their failure to win widespread adoption or to withstand the pressure for state by state variation provides less solid a basis for judging success. Indeed, such efforts may reasonably be seen as bearing fruit in cases where a Uniform Law is but one of several proposals catalyzing and shaping legislative reform. The Uniform Residential Landlord and Tenant Act might be viewed a fair success, in this light, despite its fairly limited adoption.
Model Acts are proposed laws on topics where reform not uniformity is the dominant aim. Those creating model acts contemplate that state legislatures may make alterations or even take bits and pieces. The National Conference has put forward a few Model Acts. The American Law Institute has as well. Its Model Penal Code is perhaps the best known and most influential Model Act.
Restatements are the exclusive product of the American Law Institute. They are not proposals addressed to state legislatures but rather efforts to codify or restate areas still governed by common law (judge-made law).
For more details on the Uniform Law process with an account why one particular cluster of Uniform Laws failed to win acceptance in the states, see Marion W. Benfield, Jr., Wasted Days and Wasted Nights: Why the Land Acts Failed, 20 Nova L. Rev. 1037 (1996).