This chapter looks on the evidence relating to fear as the basis of a motivational system, avoidance, and security motivation. The chapter describes the evolutionary significance of certain fears (e.g. of snakes), and the associated fast automatic processing of sensory information derived from them. The notion of a fear module is introduced. Neutral stimuli paired with a fear-evoking stimulus acquire a conditional capacity to trigger fear, as revealed in such phenomena as the conditioned emotional response. The neural model of LeDoux is described. Fear and anxiety are distinguished. A central motivational state of fear is proposed. The chapter discusses the logic behind Bolles’ suggestion of ‘species-specific defence reactions’ and the defence motivation system of Masterson and Crawford. Someone ironically, the notion of a security motivation system has been only recently developed. However, such a need was placed at the base level in Maslow’s hierarchy of needs. The chapter discusses the idea of a security motivation system as proposed by Szechtman and Woody. The chapter concludes with a discussion of when fear and security systems fail, such as in pathological anxiety.