Abstract: An adjustable threshold and sill assembly to be used at doorway entrances is disclosed. The assembly comprises a sill (preferably formed from an aluminium alloy material), a water resistant, thermally insulating front of the threshold base member which is preferably resilient but sturdy (high impact polyvinyl chloride material being preferred), means for engaging the threshold base member with the back of the sill, and an adjustable threshold member received by a rectangular channel of the base member and adjustably connected therein for upward and downward movement to vary the level of its upper surface above the open top of the channel.