Many mathematical problems, such as existence questions, are studied by using an appropriate realization process, either iteratively or continuously. This article is a collection of di erential equations that have been proposed as special continuous realization processes. In some cases, there are remarkable connections betwe e n s m o o t h o ws and discrete numerical algorithms. In other cases, the ow approach seems advantageous in tackling very di cult problems. The ow approach has potential applications ranging from new development o f n umerical algorithms to the theoretical solution of open problems. Various aspects of the recent d e v elopment and applications of the ow approach are reviewed in this article.