This paper discusses the influence of Israel Kirzner on the field of entrepreneurship research. We review Kirzner's work and argue that it contains two distinct approaches to entrepreneurship, termed Kirzner Mark I and Kirzner Mark II. Mark I with its focus on alertness and opportunity discovery has exerted a strong influence on entrepreneurship research in the last decade, and helped catapult the field forward. We propose that Mark II, with its emphasis on time, uncertainty, and creative action in pursuit of imagined opportunities, complements the discovery view and can provide an alternative conceptual grounding for the decade to come.