Many governors have launched initiatives to raise student proficiency in math and science and encourage youth to pursue careers in STEM fields (i.e., science, technology, engineering, and math). Individuals with strong STEM skills play vital roles in technological innovation and economic growth and are rewarded with more secure jobs and higher compensation throughout their lifetimes compared to those without such skills. Many obstacles stand in the way of improving STEM outcomes, not the least of which is increasing the number of students who are interested in entering the STEM pipeline. Students must be motivated to pursue STEM. They must have time, resources, and opportunities to learn and practice STEM skills. And they must see the connections between STEM knowledge and the real world so they can envision careers. Given that students in grades 1-12 spend only about 18.5 percent of their waking hours in formal classroom environments, spread across multiple subjects, there simply is not enough time for many students to learn STEM skills, apply them, and understand how they relate to potential STEM careers. Informal science can help students overcome those obstacles by generating interest in science, stimulating inquiry through organized activities outside the classroom, and exposing youth to the opportunities that STEM knowledge presents. Informal science experiences can help students see how their continued investment in STEM education opens doors to an exciting future. This paper reviews the value of informal science activities, which can occur at after-school and summer programs for children, in science centers and museums, through virtual programs over the internet, and through science competitions, to name a few examples. The paper also discusses how states can maximize the role of informal science in the state education agenda, and take advantage of a resource that can help achieve the states' STEM goals. (Contains 30 endnotes.)