Implantable devices, instruments, kits and methods for treatment of obesity. One or more devices can be implanted adjacent to or in contact with the stomach to occupy a space to prevent the stomach from expanding into that space as food is taken into the stomach. Alternatively, one or more devices may be implanted and expanded to displace at least a portion of the wall of the stomach to decrease the internal volume of the stomach that is available to receive food. Devices may be anchored to one or more internal structures at one or more locations without piercing through the wall of the stomach. Devices can be implanted using minimally invasive methods, such as percutaneous or laparoscopic methods. Delivery instruments are also provided. An intra-gastric sizing device is provided to facilitate implantation of an extra-gastric device in some method embodiments.