In United States federal courts, a circuit split, also known as a split of authority or split in authority, occurs when two or more different circuit courts of appeals provide conflicting rulings on the same legal issue. The existence of a circuit split is one of the factors that the Supreme Court of the United States considers when deciding whether to grant review of a case. Some scholars suggest that the Supreme Court is more likely to grant review of a case to resolve a circuit split than for any other reason.

Despite the desire of the Supreme Court to resolve conflicts between circuit courts, legal scholars disagree about whether circuit splits are ultimately detrimental or beneficial. Some argue that circuit splits are harmful because they create confusion and encourage forum shopping, while other scholars argue that variation among circuits allows local courts to experiment with new laws that reflect the values of the local residents. Scholars have also observed that regional variations in different areas of the United States have provided certain circuits with a particular specialization or expertise in some subjects of law.

Article III of the United States Constitution specifies that "[t]he judicial Power of the United States, shall be vested in one supreme Court, and in such inferior Courts as the Congress may from time to time ordain and establish." In 1789, Congress created the first system of intermediate appellate courts, known as federal circuit courts, which had appellate jurisdiction over certain matters decided by district courts. These federal circuit courts consisted of two justices from the Supreme Court of the United States and one district court judge. In 1891, Congress created the existing system of United States courts of appeals, which hear appeals from United States district courts within limited geographic areas. For example, the United States Court of Appeals for the Fifth Circuit hears appeals originating from United States district courts in Louisiana, Mississippi, and Texas. Decisions in circuit courts are usually made by rotating three-judge panels chosen from judges sitting within that circuit, and circuit courts also occasionally decide cases en banc.

Circuit courts do not collaborate or work with other circuits to resolve legal issues, and different circuit courts may reach conflicting conclusions about the same legal issue. Furthermore, cases decided in one circuit are not binding authority on other circuits. If the Supreme Court of the United States has not ruled on a legal issue, federal courts of appeals resolve these issues "as they see fit, subject only to a norm of intracircuit stare decisis." When a circuit split occurs, there is rarely an even numeric division among courts of appeals with regard to how the dispute should be resolved. In fact, one study found that courts of appeals split evenly in less than one third of all circuit splits. Occasionally, separate courts of appeals will reach three or more different conclusions with regard to the same legal issue.

Some scholars criticize the existence of circuit splits, while other scholars suggest that circuit splits may, in fact, be beneficial. Others simply argue that circuit splits may not be ideal, but problems associated with inter-circuit conflicts are overstated. For example, Fourth Circuit Court of Appeals Judge Harvie Wilkinson once stated the "world will not end because a few circuit splits are left unresolved."

Legal analysts have identified problems associated with circuit splits. Jesse M. Boodoo, for example, suggests that circuit splits create a state of confusion and uncertainty for citizens. Because different laws are applied and enforced in different jurisdictions, Daniel J. Meador has argued that Circuit splits may create a judicial "Tower of Babel." Additionally, Wayne A. Logan has argued that if courts speak with a unified voice, this will "secure popular respect for judicial authority." Likewise, Matthew Lund cautions that circuit splits will lead to forum shopping, where litigants flock to jurisdictions with more favorable laws. Judge Kimberly A. Moore also suggests that circuit splits and forum shopping lead to economic inefficiency because outcomes are unpredictable and litigants are less likely to settle.

Scholars have also argued that inconsistent application of laws in different circuits is inherently unfair. Trevor W. Morrison, for example, claims that circuit splits create potential due process conflicts if criminal defendants are unaware that their behavior constitutes criminal activity in that circuit. An article in the New England Journal on Criminal & Civil Confinement also suggested that there is the potential for the unconstitutional ex post facto application of law after circuit splits are resolved. Additionally, Jesse M. Boodoo argues that federal agencies tasked with enforcing laws throughout the United States may face challenges implementing regulatory measures when federal legislation is interpreted differently in separate circuits.

Legal scholars have also identified benefits associated with circuit splits. For example, Justice Louis Brandeis praised the fact that splits of opinion among courts allow jurisdictions to experiment with new developments in law without risking harm to other jurisdictions. Judge Diane P. Wood has suggested that circuit splits and "disagreements with colleagues force judges to sharpen their writing, push them to defend their positions, and from time to time persuade them that someone else's perspective is preferable". Amanda Frost has argued that negative attitudes toward circuit splits may hinder progress and creative problem solving because "[c]ourts of appeals are generally hesitant to depart from precedent set in other jurisdictions, despite being under no obligation to adhere to decisions by sister circuits." Consequently, Frost suggests that uniformity among circuits may be "overvalued." Likewise, Wayne A. Logan suggests that circuit splits may also be beneficial by virtue of the fact that citizens in different parts of the country have different preferences for how to structure their laws. Additionally, Judge J. Clifford Wallace has argued that there is nothing inherently wrong with different laws existing in different circuits, and "if conflicts were by their very nature unacceptable, the traditional rule denying precedential status to out-of-circuit decisions probably would not have enjoyed its long history."