Joinder of causes of action is a procedural device where a party may assert as many causes of action as they have against an opposing party in a single pleading. It is the process of uniting two or more demands or rights of action in one action.

The purpose of joinder is to minimize multiplicity of suits and inconvenience to the parties. It is not compulsory, but merely permissive.

The requisites for joinder of causes of action are subject to conditions, particularly when there are multiple parties or different venues/jurisdictions involved.

• The party joining the causes of action must comply with the rules on joinder of parties. This is relevant when there are multiple plaintiffs or defendants.
• Joinder shall not include special civil actions or actions governed by special rules.
• Where causes of action are between the same parties but pertain to different venues or jurisdictions, joinder may be allowed in the Regional Trial Court (RTC) if one of the causes of action falls within the RTC's jurisdiction and the venue lies therein. This specific rule applies only if the joinder is in the RTC. For joinder in the Metropolitan Trial Court (MTC), it must have jurisdiction over all causes of action and there must be a common venue.
• Where claims are principally for recovery of money, the aggregate amount claimed is the test of jurisdiction (totality rule).

When two or more causes of action are joined, each must be stated separately and prefaced accordingly in the complaint. If the answer addresses multiple causes of action, the paragraphs should also be prefaced accordingly.

Joinder of causes of action is different from splitting a single cause of action, which is prohibited and can be a ground for dismissal. It is also distinct from joinder of parties, although compliance with rules on joinder of parties is a condition for joinder of causes of action when multiple parties exist.