It has been shown that potential business benefits could be achieved by assessing and improving the requirements engineering (RE) process. However, process assessment models such as CMMI and ISO9000 only cover RE shallowly. Tailored models such as REGPG and REPM, on the other hand, do not cover market-driven requirements engineering. Other attempts such as MDREPM covers market-driven requirements engineering, but correspondingly neglects bespoke requirements engineering. Moreover, the area itself has evolved so practices that once were cutting edge are now commonplace. In this article, we develop and evaluate a unified requirements engineering process maturity model (Uni-REPM) that can be used in a market-driven as well as a bespoke context. This model is based on REPM, but has evolved to reflect contemporary requirements engineering practices. Uni-REPM is primarily created based on a systematic literature review of market-driven requirements engineering practices and a literature review of bespoke practices. Based on the results, Uni-REPM is formulated. The objective of Uni-REPM is twofold. Firstly, it is expected to be applicable for assessing the maturity of RE processes in various scenarios where an organisation would use different development approaches. Secondly, it instructs practitioners about which RE practices to perform and their expected benefits. As an assessment instrument, Uni-REPM provides a simple and low-cost solution for practitioners to identify the status of their RE process. As a guidance tool, Uni-REPM lessens the gap between theoretical and practical worlds by transferring the available RE technologies from research to industry practice.

Software products are usually developed for either a specific customer (bespoke) or a broader market (market-driven). Due to their characteristic, bespoke and market-driven development face different challenges, especially concerning requirements engineering. Many challenges are caused by an inadequate requirements engineering process, and hence there is a need for process improvement frameworks based on empirical research and industry needs. In a previous article we introduced Uni-REPM, a lightweight requirements engineering process assessment framework based on a review of empirically motivated practices in market-driven and bespoke requirements engineering literature. In this article, we validate this framework in academia as well as industry, in order to prepare Uni-REPM for widespread industry use. We conduct two validations; a static validation based on interviews with seven academic experts and a dynamic validation where Uni-REPM is applied in four industrial organisations. Uni-REPM is refined according to the feedback obtained in the validations. The study shows that Uni-REPM is a quick, simple, and cost-effective solution to assess the maturity level of the requirements engineering process of projects. Moreover, the assessment method using checklists is highly usable and applicable in various international development environments.