Search has become ubiquitous but that does not mean that search has been solved. Enterprise search, which is broadly speaking the use of information retrieval technology to find information within organisations, is a good example to illustrate this. It is an area that is of huge importance for businesses, yet has attracted relatively little academic interest. This monograph will explore the main issues involved in enterprise search both from a research as well as a practical point of view. We will first plot the landscape of enterprise search and its links to related areas. This will allow us to identify key features before we survey the field in more detail. Throughout the monograph we will discuss the topic as part of the wider information retrieval research field, and we use Web search as a common reference point as this is likely the search application area that the average reader is most familiar with.