How we understood a consumer has changed in the last quarter of a century. In the past, marketing was dominated by psychology, which is still relevant. But we understand the consumer now in terms of data. The management and analysis of data is now an important component of marketing. A statistician studied consumers by sampling, mostly a small number of say 100 people. Marketers now observe millions of consumers to draw their conclusions. They require computer science skills. Marketing is influenced by psychology, statistics and economics. Beyond that, it is also influenced by OR and computer science. One more area has acquired importance – sociology. There are groups of customers on Facebook. It is group behaviour and society behaviour which are important