In order to show the connection between a personal diary and history the author first differentiates between a diary which is a discourse and one which is a written practice. Both at the discourse level and, especially, at the written practice level, a personal diary differs from literature because of its clear relation to the context in which it was created and its specific function in the life and culture of the person keeping it - which cannot be reflected by any printed form. The article draws attention to the most important historical functions of a diary - from registering trading operations and calculating income and expenditure through recording family history, individual experiences of the world, contemplation and auto-therapy to significance as a work of literature. It includes a separate sub-chapter devoted to the material aspects of keeping diaries, suggesting that the material aspect is a legitimate part of its significance (describing material aspects, the diary supports, writing tools, the material traces of a diary being used and its fate after it is no longer being kept). At the end the author shows what research into diaries as a written practice could give rise to a new way of recording cultural history. He also draws attention to the increasing importance of private, family and public archives which keep personal documents such as diaries.