The three questions every lawsuit has to answer before its merits can be heard - whether the court has power over this kind of case (subject-matter jurisdiction), power over this defendant (personal jurisdiction), and whether this is the right place within the system to bring it (venue) - what each requires, how each is challenged, and why a judgment entered without jurisdiction is void.
Subject-matter jurisdiction is a court's authority to hear a category of case. State courts of general jurisdiction can hear almost anything; specialised state courts (probate, family, small claims, tax) are limited to their subject and often by amount. Federal courts are courts of limited jurisdiction: they can hear a case only if Congress has authorised it, principally cases arising under federal law and cases between citizens of different states (or a citizen and a foreign party) where the amount in controversy exceeds a threshold, with complete diversity required - no plaintiff may share a state of citizenship with any defendant. A defendant sued in state court on a claim the federal courts could hear may remove the case to federal court within a fixed period, subject to the rule that a diversity case cannot be removed if any defendant is a citizen of the forum state. Subject-matter jurisdiction cannot be conferred by consent or waived; the court must raise it on its own, at any stage, and a judgment entered without it is void.
Personal jurisdiction is the court's power over the particular defendant, and it is a constitutional limit rooted in due process as well as a matter of each state's long-arm statute. A court has general jurisdiction over a defendant who is "at home" in the state - an individual domiciled there, a corporation incorporated or headquartered there - for any claim whatever. Otherwise it has specific jurisdiction only if the defendant purposefully directed activities at the state and the claim arises out of or relates to those activities, so that being sued there is fair: selling products into the state, contracting with a resident to perform there, committing a tort there, or maintaining an interactive commercial presence aimed at its residents. A defendant may also be subject to jurisdiction by consent, by a forum-selection clause, by registering to do business where the statute so provides, or by being served while physically present in the state. Unlike subject-matter jurisdiction, the personal-jurisdiction objection is waived if not raised in the defendant's first response.
Venue is the question of which court within a system is the proper place for the case - which county in a state, which district in the federal system - and is set by statute, usually the district where a defendant resides or where a substantial part of the events occurred, with special rules for real property, corporations and particular statutes. Improper venue is a waivable objection; even where venue is proper, a court may transfer the case to another district for the convenience of parties and witnesses, or dismiss it under forum non conveniens in favour of a court in another country. Forum-selection clauses in contracts are generally enforced and can make an otherwise proper venue improper as between the parties. A defendant who wants to contest jurisdiction may appear specially or, in federal court, simply raise the defence by motion without conceding anything; a defendant who ignores the suit entirely and lets a default judgment enter may attack it later for want of jurisdiction, but at the price of having no defence on the merits if the attack fails.
Jurisdiction and venue decide where a case will be fought, under which procedure and before which jury pool, and that often matters as much as the merits. A defendant sued far from home - an out-of-state business, a person whose only contact with the forum was a website or a single shipment - should have a lawyer evaluate a jurisdiction motion before doing anything that could waive it, including filing a general answer. Plaintiffs choosing between state and federal court, or between counties, are making a strategic decision about judges, timelines and remedies, and the choice is difficult to reverse. Anyone signing a commercial contract should read the forum-selection clause as the term that decides where they will have to sue or be sued.
Choose your state. Each link opens the directory page for the city in that state with the most currently published law firms in this practice area; a +n beside the city is how many other cities in the state also have one. The list is generated when this page loads, so a state whose listings have lapsed drops out rather than becoming a dead link.