A civil action is a legal proceeding where one party sues another to enforce or protect a right, or to prevent or redress a wrong. (Rule 1 § 3a) The act of filing with a court of justice is what makes a claim an action or suit.

Civil actions are classified into ordinary and special. Both types are generally governed by the rules for ordinary civil actions. Special civil actions are distinguished by being subject to specific rules in addition to the ordinary rules.

Ordinary civil actions must be based on a cause of action, which is an act or omission violating another's right. This cause of action requirement does not necessarily apply to all special civil actions, such as declaratory relief or interpleader, which may be filed even without a prior violation of a right or an interest in the subject matter.

Civil actions can also be categorized based on their object or nature, including real actions (affecting title to or possession of real property) and personal actions (all others, often seeking recovery of personal property, contract enforcement, or damages). The distinction between real and personal actions is important for determining venue.

Further classifications include actions in rem, in personam, and quasi in rem. Actions in rem are against the thing itself, seeking a judgment against the whole world. Actions in personam are against a person based on personal liability, binding only the parties involved. Actions quasi in rem are against persons but seek to subject their interest in specific property to a claim. These distinctions affect how jurisdiction is acquired and the effect of the judgment.

A civil action differs from a criminal action, where the State prosecutes a person for an act punishable by law, with the primary purpose being punishment rather than compensation or redress. It also differs from a special proceeding, which aims to establish a status, a right, or a particular fact.