This study introduces a teaching portfolio as a newly recognized system for teacher professional development and performance assessment. For this purpose, the concept, functions, and application process of teacher portfolios are extensively examined by reviewing previous studies and many case projects both in Korea and other foreign countries. Especially, this study attends to the teacher portfolio project conducted for three semesters by the TESOL master's program at Sookmyung Women's University. Furthermore, this research also suggests ideas of electronic portfolios and explains the advantages of digitalizing teaching portfolios and also the most recent approach, efolio system. Finally, this research attempts to discuss the organization and entries of teacher portfolios appropriate to the Korean public school context and provide the basic principles of designing an electronic portfolio system.