A bay dog (or bailer, in Australian English) is a dog that is specially trained to find, chase, and then bay, or howl at from a safe distance from large animals during a hunt, such as during a wild boar hunt.

Bay dogs chase and circle the boar, keeping it cornered in one place, while barking intensely. This behavior is known as \"baying\" or keeping the boar \"at bay\". In Australia the terms \"bay-dogs\" and \"baying\" are not in common usage. In Australia these are colloquially referred to as \"bailers\" and \"bailing\", respectively.

The vocalizing of the dogs at bay signals the modern firearms hunter to close the distance with the pack and once caught up, to dispatch the boar with a well-placed gunshot. For the primitive weapons hunter the bay signals the hunters to release the \"catch dogs, \" that are used to then catch and hold the boar, allowing hunters to hog-tie the boar for relocation or kill the boar with a knife, spear or similar instrument. The dogs used for baying are typically curs, hounds, and various purpose-bred crosses.[1] Some crossing has occurred between \"bay & catch\" dogs, due to being raised together for generations, along with purpose-breeding. So, some \"hog dogs\" have shared traits and abilities (i.e., bay dogs capable of holding, or, catch dogs hunting by scent). But they are usually kept separate (no crossing), and used according to their own unique abilities.