The first chapter of Volume I approaches the concept of vulnerability in some of the very different streams present in psychology. Beginning with its origin in the Greek diathesis and in the Roman proclivitas, it briefly reviews the history of the emergence of the term in psychology and psychiatry. Once this is established, the chapter accepts the challenge of declaring certain qualities of vulnerability, or “the vulnerable” that are mainstream in todays scholarly work in psychology. It then distinguishes the understandings of the naturalistic and heuristic perspectives, to finally delve into the Spaniard psychiatrist Ignacio Boné Pina’s proposal in this regard. As an addition to the above, the chapter ends by developing the relation between vulnerability and stress, emotions and resilience.