Cause of action

Under the law, a cause of action is a set of facts sufficient to justify a right to sue to obtain money, property, or the enforcement of a right against another party. It means literally the cause or reason why a party can make a legal case under the law. The term also refers to the legal theory upon which a plaintiff brings a lawsuit (such as breach of contract, battery, or false imprisonment). The legal document which carries a claim is often called a Statement of Claim in English law, or a Complaint in U.S. federal practice and in many U.S. states. A complaint identifies the court's jurisdiction, the alleged facts and the relief the plaintiff wants. It can be any communication notifying the party to whom it is addressed of an alleged fault which resulted in damages. This is often expressed in amount of money the receiving party should pay or reimburse.
Filing.
To pursue a cause of action, a plaintiff pleads or alleges facts in a complaint, the pleading that starts a lawsuit. A cause of action generally includes both the legal theory (the legal wrong the plaintiff claims to have suffered) and the remedy (the relief a court is asked to grant). Often the facts or circumstances that allow a person to seek judicial relief may create multiple causes of action. Although it is fairly easy to file a Statement of Claim in most jurisdictions. If it is not done properly, then the filing party may lose his case due to simple technicalities.
There are a number of specific causes of action, including: contract-based actions, statutory causes of action, torts such as assault, battery, invasion of privacy and fraud. The points a plaintiff must prove to win a given type of case are called the "elements" of that cause of action. For example, for a claim of negligence, the elements are: the (existence of a) duty, breach (of that duty), proximate cause (legal cause), and damages. If a complaint does not allege facts sufficient to support every element of a claim, the court, upon motion by the opposing party, may dismiss the complaint for failure to state a claim for which relief can be granted.
Responding.
The defendant to a cause of action must file an "Answer" to the complaint in which the "claims" can be admitted or denied. The answer may also contain counterclaims in which the "Counterclaim Plaintiff" states its own causes of action. Finally, the answer may contain affirmative defenses. Most defenses must be raised at the first possible opportunity. Either in the answer or by motion or are considered to be waived.