One of the problems with current practice in software development is that often customer requirements are not well captured, understood and analysed, and there is no clear traceable path from customer requirements to software specifications. This often leads to a mismatch between what the customer needs and what the software developer understands the customer needs. In addition to capturing, understanding and analysing requirements, requirements engineering (RE) aims to provide methods to allow software development practitioners to derive software specifications from requirements. Although work exists towards this aim, the systematic derivation of specifications from requirements is still an open problem. This thesis provides practical techniques to implement the idea of problem progression as the basis for transforming requirements into specifications. The techniques allow us to progress a software problem towards identifying its solution by carefully investigating the problem context and re-expressing the requirement statement until a specification is reached. We develop two classes of progression techniques, one formal, based on Hoare's Communicating Sequential Processes (CSP), and one semi-formal, based on a notion of causality between events. The case studies in this thesis provide some validation for the techniques we have developed.