In the last decades there has been a growing interest towards the concept of “Quality of Life” (QoL), not only in the bio-medical field, but also in other areas, such as sociology, psychology, economics, philosophy, architecture, journalism, politics, environment, sports, recreation, advertisements. Nevertheless QoL does turn out to be an ambiguous and elusive concept – a precise, clear and shared definition appears to be a long way off. In this article an analysis of how QoL is interpreted and defined in various scientific articles published in the last two decades, is offered. In addition, an illustration of how widespread the use of this concept is in different fields of knowledge, the difficulties in reaching a shared understanding of QoL, the problems involved in stating clearly the construct, and a presentation of some of its conceptualizations, are provided. The importance of subjectivity in the definition of what QoL is, emerges as a key aspect. This personal and subjective dimension could be the starting point for a more thorough and holistic understanding of this concept, in which standardized sets of valid, reliable and evidence-based measures of, e.g., psychological and spiritual dimensions, are encompassed in the person’s quality of life evaluation.