Abstract: A firearm holster may include holster shell and a retention adjustment mechanism. The holster shell may include a first shell portion and a second shell portion defining an interior space configured to receive at least a portion of a firearm therein. The retention adjustment mechanism may be disposed at least partially between the first shell portion and the second shell portion and configured to adjust a retention level provided by the holster. The retention adjustment mechanism may include a first wedge, a second wedge, and an adjustment screw configured to cause the first wedge and the second wedge to move relative to one another to adjust a distance between adjacent portions of the first shell portion and the second shell portion.