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Supplemental means completing or making an addition to, particularly to a document - for example, a supplemental complaint, supplemental claim, or supplemental proceeding.

Some common uses of the term “supplemental” in a legal sense include:

  • In the context of pleadings, cases such as this one from Louisiana, explain that “a supplemental pleading covers issues or causes of action that have arisen since filing of original petition, which relate to issues or actions contained in original petition.”
  • In the context of jurisdiction of federal courts, cases such as this one from New York, explain that “supplemental jurisdiction is the authority of a federal court to exercise jurisdiction over a non-federal claim between parties litigating other matters properly before the court, or the addition of an independent party when the claim against that party arises out of the same common nucleus of operative facts as the claims against the other named parties.” 

[Last updated in October of 2021 by the Wex Definitions Team]