The back of the chair slides into metal rails on the base. When I first saw it, I thought it was pretty clever, but unfortunately the pieces don't fit together well and a gap is visible between the back of the chair and the arms. Additionally, the seat cushion is very firm and isn't quite the right shape for the chair, again resulting in odd gaps. It is fine for the price and I didn't want to mess with returning it as it's just an occasional chair, but I wouldn't recommend it.