Some things in our world hold together because the parts that make them up are connected to one another with a connective device. For example, the bones in our body are connected to one another by muscles, tendons, and ligaments. Other things, like the tectonic plates that make of the outer layer of Earth, remain connected because they interlock to one another at their boundaries, much like pieces of a jigsaw puzzle. Their cohesion relies entirely on contact and friction at the interfaces of their parts. The same principle can be used to build puzzle-like civil-engineering structures like arches, floor slabs, and even towers. In this lecture, you will learn more about the nice properties of puzzle-like structures and how they work, what are the challenges to bring them to more common use, and how we face these challenges.