Disclosed herein are herbicidal compositions comprising a synergistically herbicidal effective amount of (a) aminocyclopyrachlor, or an agriculturally acceptable salt or ester thereof, and (b) 2,4-D, or an agriculturally acceptable salt or ester thereof. Also disclosed herein are methods of controlling undesirable vegetation, which comprise applying to vegetation or an area adjacent the vegetation or applying to soil or water to prevent the emergence or growth of vegetation (a) aminocyclopyrachlor, or an agriculturally acceptable salt or ester thereof, and (b) 2,4-D, or an agriculturally acceptable salt or ester thereof, wherein (a) and (b) are each added in an amount sufficient to produce a synergistic herbicidal effect.