This chapter explores the psychological and marketing implications of scarcity and the Fear of Missing Out (FOMO). Scarcity, a fundamental concept in economics and psychology, drives demand by making products or opportunities appear more valuable. FOMO, prevalent in the social media age, intensifies this effect by compelling individuals to stay connected and involved. The chapter discusses how marketers leverage scarcity and FOMO through strategies like limited-time offers, exclusive access, and product drops to drive consumer engagement and sales. It also highlights the ethical considerations of these tactics, emphasising the need for transparency and consumer trust. Case studies of successful FOMO marketing campaigns by brands like Supreme, Apple, and Starbucks illustrate the effectiveness of these strategies. The chapter concludes with methods for measuring the impact of scarcity marketing, including key performance indicators and analytical tools.