The purpose of this Master’s thesis is to contribute to previous research on supplier development and to gain further knowledge on how initiatives for supplier development affect conformance quality and the business of Original Equipment Manufacturers in the automotive industry. The study was conducted at the heavy truck and bus manufacturer Scania CV AB. Two primary methods where used during the research. Quantitative data was collected through a survey targeted to 161 first-tier automotive suppliers and qualitative data was obtained by interviews with representatives of high- and low-performing suppliers. Using structural equation modelling, three hypothesized models of the expected effects of Supplier Development Programmes were tested. After analysis of the collected data, significant contributors to supplier development were derived from the findings. The main findings indicate that initiatives for Continuous Improvement have a significant and positive effect on conformance quality. Moreover, initiatives for Joint Action and Process Mapping are found to be significant contributors to supplier performance. Additionally, Scania is suggested to use a weighted Key Performance Indicator for supplier assessment, in addition to their current practice of assessing their suppliers based on the total number of quality reports.