With the looming planetary emergency, the future will be anything but an extension of the past. Yet theorizing the future poses a peculiar problem. By definition, it is not present yet. The conundrum of the future is that it requires conceptualizing and theorizing what is not (yet) observable and does not (yet) exist. Scholars have called for more impactful theories; we argue that one powerful avenue to make organizational theories more impactful is to make them more future-oriented. In this article, we call for prospective theorizing, which we define as a future-oriented approach to theorizing that is concerned with imagining desirable futures. First, we argue that prospective theorizing involves a shift along two dimensions (onto-epistemological and axiological): from projection to imagination, and from values-neutral to values-led theorizing. Second, we suggest and promote prospective theorizing practices that might enable such a shift, distinguishing between inputs, throughputs and outputs of theorizing. Third, for such prospective theorizing to be scientifically evaluable and rigorous, we develop the notion of speculative rigour, and outline criteria of generative potency, process transparency, plausible desirability and speculative plausibility. Overall, we argue that prospective theorizing adds to greater plurality in our theorizing towards (re)generative scholarship for imagining desirable futures.