The practice of hiring a recently graduated law student to serve as an in-chambers judicial assistant was pioneered by Horace Gray. Both as the chief justice of the Supreme Judicial Court of Massachusetts (1864-1881) and as an associate justice of the Supreme Court of the United States (1882-1902), Gray personally paid an assistant, whom he referred to as his "secretary." Other justices of the Supreme Court followed the practice in the late-nineteenth and early-twentieth centuries. Although Congress in 1886 heeded the advice of the U.S. Attorney General that it pay for each of the justices to hire a stenographer "to assist in such clerical work as might be assigned to him," it was not until 1919 that it provided funding for the hiring of legally trained assistants. To distinguish these assistants from the stenographers, Congress designated them as "law clerks."

The early law clerks, most of whom were graduates of the Harvard Law School, conducted legal research, checked citations, and performed a wide range of personal and administrative tasks for their judges. Despite the concerns expressed by some members of the Judicial Conference that such assistance was unnecessary or that highly paid law school graduates were not needed to perform such tasks, Congress in 1930 provided funds for each circuit court of appeals judge to appoint a law clerk. Six years later, Congress authorized district court judges to appoint law clerks as long as the senior circuit judge of the circuit in which the district was located issued a certificate of need. The number of district court law clerks was limited to 35 for the first fiscal year the statute was in effect, with no specific numerical limit thereafter. The certificate of need requirement continued until 1959, when Congress authorized judges to hire "necessary" law clerks subject to the limits of their chambers staff budgets and to the minimum law clerk salary provisions of the Judicial Salary Plan.

As federal judicial caseloads and budgets increased during the last four decades of the twentieth century, the number of law clerks retained by the judges of the federal courts rose steadily, though some judges have eschewed the practice of hiring short term law clerks in favor of "career" clerks, who are hired with the expectation that they will serve for a period of more than four years. Today's law clerks typically perform quasi-judicial functions, such as preparing bench memoranda on legal issues and composing drafts of judicial opinions.

Further Reading:
Baier, Paul R. "The Law Clerks: Profile of an Institution," Vanderbilt Law Review 26 (1973): 1125-77.

Newland, Chester A. "Personal Assistants to Supreme Court Justices: The Law Clerks," Oregon Law Review 40 (1961): 299-317.

"Law Clerks: The Transformation of the Judiciary," Long Term View: A Journal of Informed Opinion 3 (1995).