A golf club head having a slot in the sole filled with an insert in which the slot is positioned close to the striking face. The slot can be a uniform distance from the striking face or the slot can curve away from the striking face in the toe region. The insert can have a uniform height or a non-uniform height. Inserts with uniform heights can have a low height profile. Inserts with non-uniform heights can have a lower height in a central portion of the insert compared to an edge portion or a perimeter portion of the insert. The insert can also have flanges or protrusions for installation into the slot. The resulting golf club head improves performance, as the sole slot with insert allows the striking face to have a profile that meets the needs at that location.