Political scientists have traditionally approached international negotiations from a rational perspective, focusing on states as unitary actors driven by cost–benefit considerations. In this literature, the element of passing time is largely treated within the contexts of changing circumstances, discounting utility, and learning processes under conditions of incomplete information. More recent research, drawing on a behavioral political science approach, has brought attention to additional factors, such as the influence of previous decisions made by actors on their mind-sets and, consequently, on their subsequent negotiation decisions. Two behavioral effects, which focus on this impact that have successfully been integrated into the international negotiations literature, are the sunk cost effect and more recently, inaction inertia. Whereas sunk costs lead decision-makers to stick to sub-optimal conflict policies, inaction inertia drives them to continue rejecting settlement opportunities after an attractive opportunity has been forgone. Both phenomena carry important implications for ongoing negotiation processes and provide explanations for negotiation failures that are not captured by classic rational models of negotiation. This chapter discusses the concept of time in negotiations as it is treated in the negotiation research and how behavioral political science has contributed to this body of knowledge by highlighting the influence of the shadow of the past on actors’ psychological states and negotiation decisions. The chapter expands on inaction inertia in negotiations, which has more recently been introduced into the literature, presenting latest findings and methodological developments.