A stalking horse is a figure used to test a concept or mount a challenge on behalf of an anonymous third party. If the idea proves viable or popular, the anonymous third party can then declare its interest and advance the concept with little risk of failure. If the concept fails, the anonymous party will not be tainted by association with the failed concept and can either drop the idea completely or bide its time and wait until a better moment for launching an attack.

The phenomenon occurs particularly in politics, where a junior politician acts as the stalking horse to promote the interests of a senior politician, who remains unseen in case the actions would be damaging but nevertheless wants to provoke a debate or challenge to a party colleague. In some cases, stalking horses are not working for a particular individual but may wish to provoke a response that leads others to join in. In politics, the truth about the relationship between an individual stalking horse and a candidate may never be known, as both sides may claim that the (alleged) stalking horse acted without the agreement of anyone else.