The speed of thinking is a frequently overlooked aspect of mental life. However, the pace of thought is an essential property of thinking, and its consequences have recently begun to be discovered. In this chapter, we review the psychological consequences of accelerated and decelerated thought pace. We begin by examining how the manipulation of thought speed alters mood, self-perception, risk-taking, creativity, and arousal. We highlight the energizing, activating, and hedonic effects of fast thinking, and we show how thought-speed effects are independent of thought content, fluency, and goal progress. We describe an adaptive theory of thought speed wherein psychological responses to the acceleration of thinking confer adaptive advantages for confronting novel, urgent, and rapidly changing situations, and engaging in behaviors driven by appetitive motivation. Lastly, we discuss implications of thought speed and its manipulation for treatment of mental illness, for design and delivery of communications and messages, and for life in the age of rapid access and exposure to information.