Optional Defense Pacts (often referred to as ODP's) are a type of interalliance treaty wherein the signatory alliances may optionally defend each other if attacked, though such action is not required as it would be for a MDP. In practice, ODP's often function as ToA's. One variation of an ODP is the Optional Defense and Aggression Pact (oDAP/ODoAP/ODAP), wherein an alliance may both optionally defend another if attacked and optionally participate in aggressive actions with other signatories.

They are one step above ToA's and one step below MDP's on the Spectrum of Interalliance Treaties.