Prior research has highlighted that students have many conceptual difficulties regarding electric circuits and that traditional teaching methods are not successful in overcoming these difficulties. In addressing this issue, this research project placed its primary focus on the development of research based and research validated curriculum which systematically promotes the development of a scientific model for electric circuits. Over the last four years, the project focussed on developing and assessing two separate inquiry based electric circuits curricula. The first curriculum was implemented in an electric circuits module for pre-service science teachers and addressed the concept of voltage in a variety of contexts, including multiple batteries in multiple loops and RC circuits. This thesis details how the curriculum addressed the concept of voltage qualitatively and how it helped students resolve their difficulty in differentiating between voltage and current. The research also highlighted a number of newly identified difficulties pertaining to these topics. The second curriculum was implemented in a lab-based module for non-physics undergraduates. The investigation of students‘ conceptual understanding of dc circuits along with the process of adapting inquiry based curriculum to an undergraduate laboratory setting is discussed. The comparison of pretest and posttest data in both modules has shown that through the use of this curriculum the majority of students have improved their conceptual understanding of many electric circuits concepts.