Germs are always present in our bodies. However, a healthy immune system keeps them at bay and fights off illnesses that do grow in our bodies. Perhaps the most important body system, the immune system helps heal cuts and bruises and also allows the body to recover from surgery and other trauma. The main content describes the processes of the immune system through examples easily related to readers' own bodies. Full-color diagrams and photographs aid understanding as fascinating sidebars and frequently asked questions discuss some of the coolest details of this system, such as fighting infection and how broken bones heal.