In the chapter entitled “Struggle for Existence” of The Origin of Species, Darwin points out a critical assumption about evolution – that there will always be more lives than there are resources to support them. This results in constant intra- and interspecies competition in which only the fittest survive. The competition or struggle for existence occurs at the individual or organism level and, fundamentally, at the genetic level. However, advancements in knowledge since Darwin’s seminal work was published have shown further evidence that an individual’s life is composed of characteristics called life history (LH) traits. Limited resources and resource competition manifest as a limited energy budget that cannot support all LH traits, and the strategic allocation of limited energy results in trade-offs between different LH traits. Similarities and patterns derived from LH trade-offs form LH strategies, which are aimed at optimizing the struggle for existence at the individual level. One such broad pattern of LH tradeoffs is the fast–slow LH strategic continuum (Promislow and Harvey 1990). A fast LH strategy involves trade-offs characterized by early maturation and reproduction, squandering rather than conserving energy and resources, and high mating and low parenting. By contrast, a slow LH strategy involves late maturation, delayed reproduction, slow development, and a longer lifespan, all of which facilitate amassing and conserving resources, learning and developing skills, and parenting and training fewer, high-quality offspring who are equipped for intra- and interspecies competition in the struggle for existence. The fast–slow continuum and other intraindividual strategic LH trade-offs respond to and are shaped by the struggle for existence at the individual level. This chapter addresses the relationship between the environmental risks or constraints that make individuals’ lives a struggle and the intraindividual LH strategic trade-offs individuals employ to optimize the conditions of the struggle for existence.