This essay is about power in the classroom. It is about the power dimension of the student-teacher relationships that arise in that space. The overall aim has been to investigate which categories are fruitful in a power analysis of these relationships. My aim has therefore been to develop power categories and to use them to identify and to categorise cases of power interaction that take place between those particular actors in that particular setting. In order to gather material for my study I have both read literature that approaches the study of the student-teacher relationships from a power perspective and done a series of observations in a high school. My theoretical frame comprises a concept of power and a series of power categories. These categories include strength, authority, inducement, coercion, violence, resistance as well as to possess power, to have power, to exert power, the scope of power and the base of power. My theoretical definition of power is that power is the capacity to accomplish things. My operational definition is that power is the capacity of either teachers or students to accomplish change in he life of other individuals. My investigation shows that these categories are useful to deal with, classify and analyse a great number of student-teacher interactions. Other conclusions that I draw in this study are for example that power displays great variation in kind and in the situations where it occurs, that some sorts of power are more common than others, and that students’ power is more fragile than teachers’.