This article discusses 1) theoretical models of text revision, 2) skills required in revision, and 3) effects of writing support systems, including wordprocessors. Revision is not only a corrective process which comes after writing but a recursive reevaluation of the text's intended meaning and structure, occurring over the whole course of writing. Revision basically consists of detecting problems in a text and diagnosing those problems to discover ways of solving them. Diagnosing calls for more skills than detecting does. A writer's personal definition of revision has a strong influence on the processes and results of his revising; as does his ability to make a strategic use of skills and knowledge. Whereas an experienced writer tries to discover in a text what he really wants to communicate to readers and how to express that, a beginning writer identifies revision with rewording - a step which comes after he has already determined what to say. Word processors were expected to improve students' revision by reducing the physical workload in editing a text, which would encourage students to spend more of their cognitive resources in reevaluating a text's structure and coherence. Studies which examined the effects of using a word processor in comparison with pen and paper writing did not support that expectation. When a writer uses a word processor to write and revise a text, he spends less time in planning than when he uses pen and paper. Attention is focused on small segments, rather than on the whole of the text. In addition, writers find it easier to read and understand a text on paper than one on a computer display. In conclusion, also discussed are educational and technological methods for facilitating and improving revision.