My purpose in writing this article is to examine the claim that "Teachers are responsible for what happens in their classrooms" in relation to action research. Although the claim appears to be a fairly straightforward, it has multiple meanings that depend on the ideologies of those making the claim. I argue that an often-overlooked way of thinking about how teachers are responsible for what happens in their classrooms is to see responsibility as one facet of teachers' ways of being. Way of being is an existential concept that is related to the situatedness of teachers' lives, their constructions of their selves, and the ways in which they experience and conceive of freedom. This existential perspective leads me to conclude that for teachers to be aware of and to act in ways that are responsible to themselves and to their students they must be aware of their existential freedom. I conclude the paper with an examination of the ways that teachers' participation in collaborative action research can help them to become more aware of their existential freedom. The paper ends by presenting an example of action research that shows how a focus on existential concerns can illuminate the living contradictions of one's practice and identify real and mythical constraints so that one can act responsibly to help students to assume the responsibility of their own selfhood.