Abstract: The invention consists of an assembly for capping one or more exposed ends of a moulding, in particular where two elongate moulding pieces meet at a corner. The assembly consists of upper and lower rims and a web portion extending between the rims. The rims each incorporate snap-lock engagement members to releasably engage an underlying linear moulding in a sliding-type engagement. The engagement members each consist of a curved elongate flange extending from the rim, having a generally hook-shaped cross section adapted to mate with a corresponding rib extending from a linear moulding. The assembly may consist of two generally platelike separable portions that mate at the midline of the assembly to form a generally L-shaped member for installation at a room corner. The invention also consist of a combination of the corner assembly and a linear moulding having sliding engagement members adapted to mate with corresponding engagement members within the corner member.