The LL.M. programs in the United States have many unique characteristics.

In the U.S., legal training is a professional doctorate program. The first professional degree for law in the U.S. is the Juris Doctor (J.D.). Admittance to a J.D. program at an American Bar Association-accredited institution usually requires a bachelor's degree.

Admittance to an LL.M. program at an ABA-accredited institution requires a law degree—usually a J.D., but alternatively the Bachelor of Laws (LL.B.) degree if the lawyer was trained in a Commonwealth country which grants such degrees.

This leads to the unusual situation in which graduates from a U.S. institution are required to possess a doctorate before pursuing the master's degree, since there is no other first law degree in the United States. This seeming paradox has a logical historical basis: previously, U.S. law graduates obtained an LL.B. (in effect, a second bachelor's degree, after receiving a bachelor's degree to gain entry to law school in the first place) in order to qualify to take the bar. Yet, when the federal government instituted pay based, at least partially, on the level of terminal degree, lawyers were paid only at a bachelor's-level salary. So that lawyers could be paid on par with other professional-school graduates, law schools supplanted the LL.B. with the J.D., in the process hurdling the LL.M. [citation needed]

In general there are two types of LL.M. programs in the U.S.: The minority are programs involving post doctoral study of a quite specialized area of the law such as Admiralty, Tax Law, Elder Law or Aeronautical Law. The majority are programs designed to expose foreign legal graduates to the American Common Law.

As the first graduate academic degree in law in the U.S., seeking an LL.M. is common for potential law professors. While usually not a requirement for becoming a tenured professor, many professors hold an LL.M.

An LL.M. degree from an ABA-approved law school also allows a foreign lawyer to become eligible to apply for admission to the bar (license to practice) in certain states, such as New York.

Various states have different rules relating to the admittance of foreign-educated lawyers to state bar associations.

New York allows foreign lawyers from civil law countries to sit for the New York bar exam once they have completed a minimum of 20 credit hours (usually but not necessarily in an LL.M. program) at an ABA-approved law school involving at least two basic subjects tested on the New York bar exam. Lawyers from common-law countries face more lenient restrictions and do not typically need to study at an ABA-approved law school. Foreign lawyers from both civil law and common law jurisdictions, however, are required to demonstrate that they have successfully completed a course of law studies of at least three years that would fulfill the educational requirements to bar admission in their home country.[3]

California allows students who have not completed a three-year legal degree program in United States law (or, in very rare circumstances, an apprenticeship) to sit for its bar exam after completing an LL.M. in comparative law from an ABA-approved law school.

As of 2008, there is one non-ABA approved LL.M. (in international law) offered by a non-law school (The Fletcher School of Law and Diplomacy at Tufts University).