Search is an integral part of peoples’ online lives; people turn to search engines for help with a wide range of needs and desires, from satisfying idle curiousity to finding life-saving health remedies, from learning about medieval art history to finding video game solutions and pop music lyrics. Web search engines are now the second most frequently used online computer application, after email. Not long ago, most software applications did not contain a search module. Today, search is fully integrated into operating systems and is viewed as an essential part of most information systems.

Many books on information retrieval describe the algorithms behind search engines and information retrieval systems. By contrast, this book focuses on the human users of search systems and the tool they use to interact with them: the search user interface. Because of their global reach, search user interfaces must be understandable by and appealing to a wide variety of people of all ages, cultures, and backgrounds, and for an enormous variety of information needs.

The truly worldwide reach of the Web has brought with it a new realization among computer scientists and laypersons alike of the enormous importance of usability and user interface design. In the last ten years, much has become understood about what works in search interfaces from a usability perspective, and what does not. Researchers and practitioners have developed a wide range of innovative interface ideas, but only the most broadly acceptable make their way into major Web search engines.