This paper describes a novel search history tool and a set of iteratively developed user interface design guidelines for search histories that support information seekers executing complex search tasks. Search histories have a great potential in search support; however, they are usually ignored by designers and researchers in information retrieval (IR) user interface design and not integrated well into IR systems. In prior research by the first author (Komlodi, 2002), both user reports and researcher observations revealed that searchers need this type of historical information in information seeking, but find it hard to remember all historical information that is necessary. To complement their memory, information seekers often create external search history representations. To address the lack of adequate system support in this area, we describe an integrated search history tool that was developed based on the results of an extensive user study of attorneys and law librariansí memory use in searching. This tool has been iteratively refined through a cooperative design process and two cycles of usability evaluations. The tool has two main parts. An integrated and interactive search history display is proposed with user annotations and marking. The history displays details of search steps and can be selectively edited by users. An additional notepad area affords flexible results collection and early integration via user annotations and notes. The evaluation showed great promise in providing improved search history support for information seekers. The results of the evaluation validated the user interface design guidelines for search histories. It is hoped that these results will enable the designers of IR systems to better integrate historical information into their systems and provide improved support for users.