Abstract: A rigid insulating panel has a plurality of surface elements and four edges. At least two of the four edges have a connecting member including a tongue and groove assembly engageable with the tongue and groove assembly of an adjacent insulating panel to maintain the panels in engagement. The connecting members of the at least two of the four edges further include an alignment assembly wherein at least one of the connecting members includes at least one alignment projection protruding in its groove and at least another one of the connecting members includes at least one alignment recess defined in its tongue. The at least one alignment projection is insertable in the at least one alignment recess to laterally align engaged ones of the adjacent insulating panels. A rigid insulating panel assembly includes at least two rigid insulating panels with the above characteristics.