Can you imagine a world without teenagers? Before the early 1900s, the word teenager was not even part of the American vocabulary. The concept of adolescence--those transitional years between childhood and adulthood--simply did not exist. Instead, families needed young people to contribute to the family's earnings as soon as possible. "Everybody worked; it was a part of life, for there was no life without it," wrote Edna Matthews Clifton of her teen years in Texas in the late 1800s. Many young people worked longs days and full weeks on farms or in factories. Such a schedule left little time for school or for fun. Throughout the 1900s, the idea of the teenager gradually began to take shape. A series of reforms put restrictions on child labor. Young people spent less time working and more time in school. They also began spending money on entertainment. Movie theaters and dance halls provided places for them to gather. Thirteen- to nineteen-year-olds established a unique culture that would continue to develop in the coming decades. In the twenty-first century, teens represent vital threads in the American fabric. Their spending choices affect both the economy and the way advertisers market products. Their taste in music, movies, and TV drives pop culture. And teens--for whom technology is a way of life--are the ones who will continue to push the boundaries of our technological future. From the flappers and jazz babies of the 1920s to the digital-savvy teens of the twenty-first c