This self-study documents two teacher educators' professional inquiry into the notions of critical friendship. Specifically, we asked: How does our interactive inquiry on the topic of critical friendship lead us to new understandings of critical friends? Three theoretical perspectives framed this study -- More Knowledgeable Others, Thought Collective, and reflection. Data sources included (a) artifacts from the self-study scholarship/literature, (b) written and real-time (audio recorded) dialogue, and (c) critical friend response memos. We systematically analyzed our data, linking the initial themes to our theoretical frame. These themes led to three findings about critical friendship: flexible definitions, complex characteristics, and multiple learning phases. Based on these findings, we created two research tools useful for researchers enacting critical friendship -- the Critical Friend Definition Continuum and the Critical Friend Guide for Quality Assurance. Ultimately, we assert that we, along with our colleagues, must be responsible brokers of critical friendship by explicitly explaining our purposes, definitions and uses of critical friendship within our work as self-study researchers.