Every large thing in the universe is made up of smaller components. To make things like stars, planets, plants, and people, enough of the interstellar medium has to come together and interact—physically, chemically, and even biologically—to create them. In other words, we here on Earth are part of the interstellar medium. So to understand our origins and ourselves, we must understand the interstellar medium, which includes the basic building blocks of everything we see in the cosmos.