<P>Big Data is made up of lots of little data: numbers entered into cell phones,addresses entered into GPS devices, visits to websites, online purchases, ATM transactions, and anyother activity that leaves a digital trail. Although the abuse of Big Data -- surveillance, spying,hacking -- has made headlines, it shouldn't overshadow the abundant positive applications of BigData. In <I>Reality Mining</I>, Nathan Eagle and Kate Greene cut through the hype andthe headlines to explore the positive potential of Big Data, showing the ways in which the analysisof Big Data ("Reality Mining") can be used to improve human systems as varied as politicalpolling and disease tracking, while considering user privacy.</P><P>Eagle, a recognizedexpert in the field, and Greene, an experienced technology journalist, describe Reality Mining atfive different levels: the individual, the neighborhood and organization, the city, the nation, andthe world. For each level, they first offer a nontechnical explanation of data collection methodsand then describe applications and systems that have been or could be built. These include a mobileapp that helps smokers quit smoking; a workplace "knowledge system"; the use of GPS,Wi-Fi, and mobile phone data to manage and predict traffic flows; and the analysis of social mediato track the spread of disease. Eagle and Greene argue that Big Data, used respectfully andresponsibly, can help people live better, healthier, and happier lives.</P>