This paper describes the development of a continuous-time signals and systems concept inventory (CT SSCI) exam. The CT SSCI exam has twenty-five multiple choice questions and is designed to assess students' understanding of core concepts in undergraduate signals and systems. The questions require little or no computation, and contain distractors, or incorrect answers, that capture common student misconceptions. This paper discusses the list of concepts covered by the exam, reviews test results for the first version of the CT SSCI, and describes the question design strategy. A study to evaluate version 2.0 of the exam is underway at four campuses, and this paper reports preliminary results from that study.