Stars are one of the most frequently covered topics in introductory astronomy classes. From a constructivist framework, one must know what conceptions students bring with them to the classroom in order to effectively facilitate deep conceptual learning about stars. This study investigated the beliefs about stars that students hold when they enter an introductory astronomy course, and used that information to develop a concept inventory that can be used to assess those beliefs pre- and postinstruction.First, students' preinstructional beliefs were investigated through the use of student-supplied-response (SSR) surveys, which asked students to describe their ideas about topics such as what is a star, how is starlight created, how are stars formed, are all stars the same, and more. More than 2,200 students participated in this portion of the study during four semesters. Responses were inductively analyzed in an iterative process and coded for themes. Calculated frequencies show that although many students (80%) understand that stars are made of gas, a third to half of the participants (32-44%, depending upon the question) believe that starlight is created (or energy otherwise emitted) as a result of the star burning. Nuclear fusion, the true energy source in stars, is identified by fewer than 10% of the students. Interviews with seven volunteers confirmed that the responses seen on the SSR surveys were consistent with verbal explanations.The second portion of the study involved the design and testing of the Star Properties Concept Inventory. After item development and testing on Versions 1 and 2, interviews with 18 participants about their responses to Version 1, and an expert review by 26 volunteer astronomy instructors, Version 3 was created and tested during the Fall 2005 semester. Results from approximately 2,000 students who took Version 3 show that those students in an introductory astronomy course for nonscience majors increased their scores significantly over the semester, whereas a control group (students in an introductory earth science course for nonscience majors) showed no increase. These results support the purpose of this concept inventory to investigate the effectiveness of instruction on the topic of star properties and formation.