This book case is a sliding door. It is about three inches thick. The skirting on the bottom is open, allowing my 15 pound dachshund, Madison, to walk through. The books are actually cut to a depth of 2 inches. More books have been added since this picture was taken. The construction is pine board with dove tail corners. the shelves are fitted with sliding dove tail joints.The skirting has mitered edges. The back is oak faced quarter inch plywood (on the opposite side) with the back painted flat black ( as seen here) to aid the illusion that it is a real book case. The books are glue in place.