Before slavery was abolished in the United States, more than 100,000 slaves escaped to freedom with help from the Underground Railroad. A secret network of safe houses, the Underground Railroad is an important part of American history. Underground Railroad workers such as Harriet Tubman and Frederick Douglass devoted their energy and even risked their own safety to help enslaved blacks escape to freedom. Additional features to aid comprehension include a table of contents, informative captions and sidebars, a phonetic glossary,a time line, a Think-About-It section, and an index.