Civil procedure in the United States consists of rules that govern civil actions in the federal, state, and territorial court systems, and is distinct from the rules that govern criminal actions. Like much of American law, civil procedure is not reserved to the federal government in its Constitution. As a result, each state is free to operate its own system of civil procedure independent of her sister states and the federal court system.
History.
Early federal and state civil procedure in the United States was rather ad hoc and was based on traditional common law procedure but with much local variety. There were varying rules that governed different types of civil cases such as "actions" at law or "suits" in equity or in admiralty; these differences grew from the history of "law" and "equity" as separate court systems in English law. Even worse, discovery was generally unavailable in actions at law. In order to obtain discovery, a party to a legal action had to bring a collateral proceeding, a bill in equity in aid of discovery, just to obtain essential documents or testimony from the opposing party.
Procedure in the early federal courts was rather incoherent. The Process Act of 1792 authorized the federal courts to write their own procedural rules for everything but actions at law. In the context of actions at law, the earlier Process Act of 1789 was so poorly written that it forced a federal court sitting in a state to apply the common law rules of pleading and procedure that were in effect in the state at the time it joined the Union, regardless of whether the state had modified or revised its civil procedure system since. In other words, even though a state's common law pleading system was always constantly evolving through case law, the federal courts in that state were literally frozen in time (a concept now known as "static conformity"). The Process Acts of 1789 and 1792 did not expressly address the problem of what procedural laws to apply in the federal courts in new states that joined the Union after the original Thirteen Colonies. In 1828, Congress enacted a law which stated that such courts would follow the civil procedure in effect at the time those states joined the Union.