In civil procedure, a complaint is the initiatory pleading that states the plaintiff's or claiming party's cause or causes of action. It must include the names and residences of the plaintiff and the defendant. As an initiatory pleading, it requires the payment of docket fees and typically includes a certification against forum shopping. The nature of the action is determined by the allegations within the body of the complaint, not its caption or the relief sought. A complaint must allege ultimate facts constituting the cause of action. Failure to state a cause of action in the complaint is a ground for dismissal.

In criminal procedure, a complaint is a sworn written statement charging a person with an offense. It is subscribed by the offended party, any peace officer, or other public officer charged with the enforcement of the law. It is filed in court to initiate criminal prosecution for crimes usually cognizable by the Municipal Trial Courts (MTC) or Municipal Circuit Trial Courts (MCTC). A complaint can also be filed with the office of the prosecutor for preliminary investigation. For private crimes or those not prosecutable de oficio, the complaint must be filed by the offended party. A complaint is sufficient if it states the name of the accused, the designation of the offense, the acts or omissions constituting the offense, the name of the offended party, and the date and place of commission. Sufficiency is determined by whether the hypothetically admitted facts alleged constitute the elements of the offense.