An indexer organizes information and creates an index which can be used to locate that information. Every time someone opens a nonfiction book and flips to the index to look something up, she or he is taking advantage of an indexer's hard work. Indexers can index books, magazine articles, and other types of publications. They may also provide abstraction and databasing services, depending on their skill sets and the areas in which they work.

Conventionally, authors are responsible for their own indexing. However, indexing is a highly specialized skill, and most authors are not up to the task. Hence, they refer the job to an indexer. Indexers commonly work as freelancers, doing work on a job by job basis. Some may work for publishing companies, with large publishing houses maintaining a staff of indexers. The advantage to working as a staff indexer is steady employment along with access to style guidelines which can be helpful when developing an index.

Although computer programs can try to create an index for a book, it usually takes the skills of an indexer to do the job right. Computers are very good at concordance, in which the computer identifies where specific words or phrases appear, and some are intelligent enough to determine how relevant an appearance is, but computers can still make mistakes.

An indexer reads through a book, receiving proofs which include final page numbers. The indexer takes notes of key phrases and words and where they appear to start building an index. Working as an indexer is tricky, because the indexer must think about the needs of an audience, determining what kind of terms people might want to look up. He or she must think about where people might look for a term; with a cookbook, for example, someone who wants a recipe for carrot cake might look for either “cake, carrot” or “carrot cake,” and the indexer needs to decide what would be most appropriate. Indexers also need to have consistent style. In other words, if “cake, carrot” is being used, than any cake entry in the index would be formatted this way, as in “cake, chocolate,” “cake, marble,” “cake, angel food,” and so forth.

The finished index is submitted to the publisher, and the publisher adds it to the finished publication so that it can be printed and distributed. The document is also usually reviewed to confirm that it will work with the publication and be appropriate for the audience. The author, for example, might scan it to make sure that key topics are covered in the index. In a book about nutrition, for example, one might expect to be able to find terms like “calories,” “diet,” “nutritional values,” and so forth in the index.

Indexers can receive training through indexing certification classes and seminars. Some community colleges and technical schools also offer this type of training. Membership in a professional organization is open to people with demonstrated skills, and can be useful for people who would like to build professional careers as indexers.