This 2021 Edition has been meticulously developed to cover the requirements of the Middle Years Program of the International Baccalaureate. We’re grateful to both teachers and students for your ongoing feedback on our content. This feedback has shaped our 2021 edition in every possible detail - through this collaborative effort we have delivered the quintessential textbook experience in a wholly online environment, taking full advantage of the digital medium to craft a comprehensive teaching and learning resource. Planning a lesson, teaching the material, monitoring participation, and reporting on progress are all enhanced by a range of integrated features. These serve to liberate teachers from tedium and distraction, allowing them to focus their time and effort on fostering authentic learning and connecting with their students. This work has been developed independently from and is not endorsed by the International Baccalaureate Organization. International Baccalaureate, Baccalauréat International, Bachillerato Internacional and IB are registered trademarks owned by the International Baccalaureate Organization.