Databases are not the only means for the storage. Documents are also information repositories, often referred to as semi-structured data, forming the backbone of the Web. Information retrieval is concerned with finding such material (documents) of an unstructured nature (text) that satisfies an information need from within large collections. Work has gone on for at least a decade on how to manage and find documents in the web, how to structure and navigate large collections, and how extract information from text sources. This module introduces topics related to information retrieval systems and web search.