Context. The empirical study of Somerville in 2005 has shown that potential business benefits could be achieved by assessing and improving the Requirement Engineering (RE) process. However, currently there has not been an adequate instrument for practitioners to perform this work. Most known process assessment models such as CMMI and ISO do not pay intensive attention on RE whereas tailored models such as GPG and REPM do not cover the mentioned area extensively. Objectives. This thesis presents a conceptual research of RE process assessment in which the researcher aims to develop a practical model for evaluating the maturity of RE processes in industrial settings. Methods. A major part of this study consists of a systematic review and a literature review to explore all RE ―good practices‖ as a profound basis for the new model. Together with identifying potential activities, the two reviews also highly regarded the feasibility of certain practices and their context to assure the validity of the model. Conclusions. Based on the results of the reviews, Uni-REPM is formulated and introduced. 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 organization would use different development approaches. Secondly, it instructs practitioners with what to perform in RE processes and what they would benefit from such activities. As an assessment instrument, Uni-REPM serves a simple and low cost solution for practitioners to identify the status of their RE process. As a guidance tool, Uni-REPM is believed to lessen the gap between theoretical and practical worlds by transferring the available RE technologies from research to real work.