Project Blue Book was a job where some people in the United States government looked at things in the sky and tried to figure out what they were. Sometimes people thought they saw things like spaceships from outer space, and the people in Project Blue Book wanted to know if that was true or if there was a different explanation. They talked to lots of people who saw things in the sky and wrote down what they found out. Even though Project Blue Book ended a long time ago, some people still talk about it today because they like to think about what might be in outer space.