A conditioner (or hay conditioner) is a farm implement that crimps and crushes newly cut hay to promote faster and more even drying. Drying the hay efficiently is most important for first cutting of the hay crop, which consists of coarse stalks that take a longer period of time to draw out moisture than finer-textured hays, such as second and subsequent cuttings.

A conditioner is made up of two grooved rollers which the hay is forced through, causing the stalks to split, thus allowing the liquid trapped behind cell walls (sap and cell sap) to leak out and also giving more surface area for evaporation. The stand-alone conditioner is no longer used on most farms, since the conditioner has been incorporated into mower-conditioners, which combine the mower and conditioner into a single machine. The names Haybine and Discbine are brand names of mower-conditioners, although some farmers use these names somewhat generically.