Book excerpt: We are all familiar with the summative, Ofsted model of lesson observation where performance is judged according to external criteria. However, used formatively and creatively, lesson observation is a process that can support and professionally develop the observer as much as the observed. Observing colleagues teach and allowing them to observe us teach are among the most valuable and effective ways of improving our own practice. This is a practical book for all teachers. It covers being observed; learning to be a good observer - whether that's to coach the colleague you are observing, to learn from what you see or to assess performance; participant observation; pair and trio observation; feedback; pupil observation and personalising observation for your own school/department/subject.