‘Nature’ vs. ‘nurture’ is a paradigm that has been known for a long period of time. With the human genome project completed in 2001, scientists expected that the information contained in our genes would demystify the concept of ‘nature’ vs. ‘nurture’. However, the sequencing the human genome had generated more questions than answers. Humans are ~99.9% identical in their DNA sequence, with the remaining 0.1% difference often referred to as genetic variants. Those variants partly explain the heterogeneity between individuals in a variety of visible (i.e. eye colour) or invisible (i.e. health and exercise-related) traits, termed phenotypes. The type and magnitude of physiological adaptations to exercise training stimuli are highly variable between individuals, and is influence by genetics and environmental factors, and the combination between both (epigenetics). In this chapter, we summarize the efforts to date in the area of genetics and epigenetics in deciphering the paradigm of ‘Nature’ vs. ‘Nurture’ and training adaptations.