Collaboration is often required for activities that are too complex or difficult to be dealt with by a single individual. Many situations requiring information-seeking activities also call for people to work together. Often the methods, systems, and tools that provide access to information assume that they are used only by individuals working on their tasks alone. This review points to the need to acknowledge the importance of collaboration in informationseeking processes, to study models, and to develop systems that are specifically designed to enable collaborative information seeking (CIS) tasks. This chapter reviews the literature from various domains including library and information science, human-computer interaction, collaborative systems, and information retrieval. Focus of the review is on the extent to which people work together on information seeking tasks and the systems and tools that are available for them to be successful. Since CIS occurs in the broader context of collaboration in general, a review of literature about collaborations is first undertaken to define it and place it into context with related terms such as cooperation and communication. A more focused review of research follows relating CIS to systems that have attempted to support such interactions. Included are identification and synthesis of a number of core issues in the field and how best to evaluate systems and collaborative tools. Key lessons learned from the review are summarized, and gaps in the literature identified to spur future research and study.