Pedagogical content knowledge refers to a teacher's understanding of how to effectively structure and represent academic content for students based on an understanding of common misconceptions and learning difficulties. It builds on content knowledge of a subject area as well as pedagogical knowledge of teaching strategies. Effective teaching requires the flexible integration of content knowledge, pedagogical knowledge, and increasingly, technological knowledge. As technologies continue to evolve, they present new challenges for teachers to apply them in straightforward and stable ways. The three core components of a teacher's knowledge - content, pedagogy, and technology - are interlinked and influence one another. Teachers must be aware of these three knowledge domains to identify and address problems in education.