Bones are more than just the scaffolding that holds the body together. Bones come in all shapes and sizes and have many roles. In this article, we explain their function, what they are made of, and the types of cells involved. Despite first impressions, bones are living, active tissues that are constantly being remodelled. Bones have many functions. They support the body structurally, protect our vital organs, and allow us to move. Also, they provide an environment for bone marrow, where the blood cells are created, and they act as a storage area for minerals, particularly calcium. At birth, we have around 270 soft bones. As we grow, some of these fuses. Once we reach adulthood, we have 206 bones. The largest bone in the human body is the thighbone or femur, and the smallest is the stapes in the middle ear, which are just 3 millimetres (mm) long. Bones are mostly made of the protein collagen, which forms a soft framework. The mineral calcium phosphate hardens this framework, giving it strength. More than 99 percent of our body’s calcium is held in our bones and teeth. Bones have an internal structure similar to a honeycomb, which makes them rigid yet relatively light.