Louisiana attorneys who’ve been displaced by Hurricane Katrina are worrying about whether they’ll know enough to pass the bar exam in another state. Meanwhile, law students from New Orleans who transfer out of state won’t be able to take the courses they need to practice in Louisiana. What makes Louisiana law unique?

Napoleon. The legal system in Louisiana—unlike that of any other state—derives from the Civil Code established by the French emperor in 1804. Four years before Louisiana became a state in 1812, the former French and Spanish colony adopted a version of the Napoleonic Code. (Some people say it’s wrong to call Louisiana’s legal system “Napoleonic,” since the state Civil Code was also influenced by Spanish law. Historians still argue over the extent of this Spanish influence.) The resulting system of “civil law” in the state differs from the other 49 states’ “common-law” traditions in terms of methodology. Rulings in the French-influenced system derive from direct interpretation of the law; rulings in the common-law system give greater authority to legal precedent.

In theory, a judge in Louisiana decides a case based on her own interpretation of the code, not those of prior courts. In the other states, judges are supposed to make decisions based exclusively on previous rulings. But in practice, the two systems often work the same. Louisiana judges have the benefit of 200 years of case history, even if case law isn’t used as the fundamental basis for their rulings. And judges in other states can stray from a legal precedent if they deem it grossly unjust.

Specific laws also reflect Louisiana’s Spanish and French roots. For example, the principle of “forced heirship“—that a child is legally guaranteed a share of his parents’ estate—comes from the Napoleonic Code and does not appear on the books in any of the 49 common-law states. Similarly, some laws governing commercial transactions in Louisiana come from the French system, putting them at odds with the parts of the Uniform Commercial Code used by other states.

Students at Louisiana law schools who plan to go into practice elsewhere may choose to focus on “American law” instead of the Louisiana Civil Code *. The state bar doesn’t offer reciprocity with that of any other state, so there’s no way to practice law in Louisiana unless you pass the Louisiana bar exam.

Next question?

Explainer thanks Randy Trahan of Louisiana State University and reader Barbara Rose Shuler for asking the question.

Correction, Sept. 13, 2005: This article originally implied that Louisiana law students can choose to study common law in addition to required classes on the Louisiana Civil Code. Many law students in the state choose to focus on common law instead of the Louisiana code. Return to the corrected sentence.