This dissertation consists of three related essays that contribute to the microfoundations of strategy and the upper echelons perspective in particular. The first essay (Chapter 2) unpacks the psychological mechanism through which top management team (TMT) gender diversity lends strategic advantages to firms. The findings reveal a unique interpersonal mechanism (TMT psychological safety) that mediates the positive effect of TMT gender diversity on firm ambidexterity. This mechanism highlights the gender-specific interpersonal benefit of TMT gender diversity, which is markedly distinct from the cognitive-variety mechanism that has been associated generically with TMT demographic diversity including gender. The second and third essays (Chapters 3 and 4) then move beyond the demographics of upper echelons and explore a fundamental yet under-investigated psychological aspect—their subjective constructions of time (i.e., subjective time). Because conceptualizations of subjective time have been ambiguous and fragmented in strategy and other organizational fields, Chapter 3 advances a conceptual clarification and integration of extant temporal concepts in organizational research. Specifically, we offer a framework that integrates the temporal concepts into four archetypes of subjective time (individual temporal disposition, individual temporal state, collective temporal state, and collective temporal disposition). Then, we illustrate the distinct conceptual nature and theoretical implications of each temporal archetype. Building on a better conceptual base, Chapter 4 introduces a new concept of individual temporal disposition—a CEO’s temporal ambivalence. This concept captures a CEO’s deeply ingrained tendency to simultaneously attend to the present and future in strategy making, which sheds light on a dispositional account of firms’ heterogeneous strategic choices in the face of intertemporal tensions. In this chapter, I show that CEO temporal ambivalence facilitates firm ambidextrous innovation through shaping the CEO’s attitude toward contradictions and perception of complex causality. Collectively, this dissertation advances upper echelons research on two fronts: (a) by unpacking the psychological mechanisms underlying the executive characteristic–firm outcome relationship, this work promotes the theoretical depth of upper echelons research; and (b) by venturing upper echelons inquiries into the largely uncharted territory of subjective time, this dissertation also adds to the theoretical breadth of upper echelons research.