This article explores teachers' beliefs and attitudes in relation to the implementation of portfolios and their contribution to professional development in Malta. Based on the results of a mixed methods study, the article demonstrates that in order for the implementation of a portfolio system to cultivate professional development teachers' beliefs and attitudes need to be adequately examined. Through an investigation of such beliefs and attitudes, this study highlighted a number of issues that need to be considered in order to maximize the benefits of portfolios. Such research is necessary because itprovides an opportunity to foreground teacher agency with respect to effective portfolio implementation and use.