If we let the human realities that accompanied those older tools fall into oblivion, if the arrival and actual or potential disappearance of e-mail, laptops, and so on become just a set of distant facts, then we lose a part of our humanity, a historical sense of our recent selves. We have witnessed stunning transformations of society, politics, communication, and even selfhood. New identities have emerged or been fabulously empowered—the angry citizen with a video camera handy, the hyper–social networking teenager, the blog “troll,” avatars. To understand them, to judge them well, we need steady and penetrating reminders of the changes they have wrought. The writers included here provide just that.