These methodologies for predicting and shaping our behavior have grown more sophisticated over the first two decades of the twenty-­first century. Collection and analysis of big data about people is a well-­established industry. It includes the companies collecting data (miners), those trading it (brokers) and those using it to generate advertising messages (marketers), often with overlap between all three. It can be hard to obtain reliable estimates of the size of the industry, given its complexity, but one study says that by 2012 it was worth around $156 billion in the United States and accounted for 675,000 jobs. It has undoubtedly grown since then. Like slum landlords who rent out dilapidated apartments, or greedy hotshot developers who take advantage of legal loopholes to build luxury condos, companies that trade in personal data represent the sleazy side of how digital technology is impacting the real estate of our minds. This industry uses the faux luxuries of choice and convenience to entice us to part with our data, but often what they are really selling is overpriced and dodgy.