Particularly in the context of large software systems, prevention and early detection of errors during product development are critical factors in controlling cost and quality. Top-down design, structured programming, informal program verifications, and code inspection are some of the tools presently being used in order to reduce the probability of error. However, current methodologies fail to provide a systematic, comprehensive and well formalized error-detection strategy. In response to this need, a new software development methodology is proposed. The approach, described in the next section, incorporates a cohesive set of verification procedures that enables the validation of each development stage, from requirements definition through individual program implementation. The description of the verification procedures is part of the third section, while the fourth section deals with some managerial aspects related to the practical implementation of the advocated techniques in an industrial environment. A summary and conclusions are presented in the fifth section.