Injection devices are tools used to deliver medications or vaccines directly into the body. Common types include syringes, auto-injectors, and pen injectors. These devices can administer various substances, such as insulin for diabetes or vaccines for preventable diseases. Most injection devices are designed for single use to ensure safety and prevent infection. They come in different sizes and designs to accommodate various needs, from self-administration to professional healthcare settings. Proper training and technique are essential for effective and safe use of these devices.