When there is more than one state, or more than one jurisdiction (state court, federal court) with a significant relationship to the parties and circumstances involved in a lawsuit or dispute, the question may arise as to which state or jurisdiction’s laws will govern the lawsuit or dispute. The body of law that determines what law governs a dispute is called conflict of laws and consists of legal principles courts use to determine which state or jurisdiction’s law applies—unless the parties to a dispute have agreed (usually in a contract) on what law will apply.

In Iowa, as in other states, the issue of which jurisdiction's laws apply to a lawsuit or dispute is governed by the principles of 'conflict of laws' or 'choice of law.' These principles are designed to resolve questions of which state or jurisdiction's substantive law should be applied in cases where the parties or the circumstances of the case have connections to more than one jurisdiction. Iowa courts will typically use a 'most significant relationship' test to determine which state's laws are most appropriate to apply to the issues in the case. This involves evaluating factors such as where the parties reside, where a contract was executed or where a tort occurred. Additionally, Iowa courts will honor choice of law clauses in contracts where the parties have agreed in advance to the application of a particular jurisdiction's laws, provided that the chosen law has a substantial relationship to the parties or the transaction and is not contrary to a fundamental policy of a state with a materially greater interest. When federal law is involved, the court will determine whether federal or state law applies based on the nature of the legal issue, with federal law typically prevailing in matters of federal concern due to the Supremacy Clause of the U.S. Constitution.