This study investigated novice science and mathematics teachers' beliefs about planning and implementation of project-based instruction. Data for this qualitative study included two focus groups and a questionnaire. Items in the questionnaire were designed using preliminary findings from the analysis of the two focus groups, and from predefined items from the National Survey of Project Based Learning and High School Reform. The questionnaire was administered to 138 novice secondary mathematics and science teachers certified in their respective content areas. The respondent rate was 70% (n = 96). Of the 96 respondents only 28 participants utilized project-based instruction. Data analysis revealed that the 28 participants held two specific beliefs about project-based instruction. First, participants believed that the implementation and enactment of PBL: (a) made student learning more personalized by specifically meeting the individual interests or needs of students; (b) promoted students' international or cross-cultural understanding; (c) promoted students' civic engagement and contributions to the community or world; and (d) impacted high-achieving students ability levels. Second, participants believed that the implementation and enactment of PBL: (a) made teaching and learning more varied, challenging, or fun; (b) taught skills beyond academic content; and (c) taught academic content knowledge and skills more effectively. These two beliefs were situated within contexts where the instructional strategy most often used to deliver content was direct instruction and by external factors that impacted the participants' utilization and implementation of PBL. External factors included: testing and accountability requirements; a lack of time for planning and implementation of PBL lessons; students' lack of experience or skills associated with enactment of PBL; large class sizes; limited classroom space; and poor attendance.