Very easy to put together...well, that's after I've done 5 of them in various sizes. There are plastic collars that fit into indentations (spaced one inch apart) on the upright support rods. If you look closely at the collars, there is an "up" side. When you slide the shelves down over the collars, the weight of the shelves (and a little help pushing them down) forces the collars to to wedge themselves into the tubular ends on all four corners of the shelves. When you get all the shelves in place, the stability is good and the unit is very strong. I'm using this one under a window to store kitchen appliances I don't use often and "S" hooks to hang things like griddles and woks. Works great, is inexpensive storage, and I can pretend I'm on Cutthroat Kitchen. :-)