Abstract: A generally rectangular insulating block presenting parallel and opposite upper and lower surfaces and end and side portions thereof. A first series of matching dovetail mortises and tenons are provided on the end portions with a second series on the side portions. The mortises and tenons provide for interlocking of adjacent blocks in a particular wall course. A plurality of regularly spaced sockets are formed in the bottom surface of the block into which may be frictionally engaged a like plurality of regularly spaced posts on the top surface of subjacent blocks in a lower wall course. Additionally provided is an insulating wall including at least two of the insulating blocks of the present invention angular in superimposed courses of interlocking adjacent blocks.