Super easy to put together.  As I was taking out of the box, both kitties were very curious.  As soon as it was put together, one was climbing up to the top, quickly followed by the other who declared that the top perch belongs to him.  Assembly took between 5-10 minutes.  My only wish is that the bottom trunk was covered with sisal so that they can scratch it.  But I can readily add that with some rope and a hot glue gun.