Electricity and magnetism are important topics in physics. Research shows that students have many common difficulties in understanding concepts related to electricity and magnetism. However, research to improve students' understanding of electricity and magnetism is limited compared to introductory mechanics. This thesis explores issues related to students' common difficulties in learning some topics in electricity and magnetism and how these difficulties can be reduced by research-based learning tutorials. We investigated students' difficulties in solving problems involving light bulbs and equations involving circuit elements. We administered multiple choice questions and essay questions to many classes and conducted individual interviews with a subset of students. Based on these investigations, we provide suggestions to improve learning. We also developed and evaluated five tutorials on Coulomb's law, Gauss's law and the superposition principle to help students build a robust knowledge structure and firm understanding of these concepts. Students' performance on the corresponding pre- and post-tests indicates that these tutorials effectively improved their understanding. We also designed a Magnetism Conceptual Survey (MCS) that can help instructors probe students' understanding of magnetism concepts. The validity and reliability of this MCS is discussed. The performance of students from different groups (e.g. female students vs. male students, calculus-based students vs. algebra-based students) was compared. We also compare the MCS and the Conceptual Survey of Electricity and Magnetism (CSEM) on common topics.