Apache Hadoop, the popular data storage and analysis platform, has generated a great deal of interest recently. Large and successful companies are using it to do powerful analyses of the data they collect. Hadoop offers two important services: It can store any kind of data from any source, inexpensively and at very large scale, and it can do very sophisticated analysis of that data easily and quickly. Hadoop is different from older database and data warehousing systems, and those differences can be confusing to users. What data belongs in a Hadoop cluster? What kinds of questions can the system answer? Understanding how to take advantage of Hadoop requires a deeper knowledge of how others have applied it to real-world problems that they face. This paper presents ten real-world Hadoop use cases. These are, of course, examples. One or more may apply directly to your business, but they are only a small sample of the ways that companies are using Hadoop today.