Since its first use in the 1960s, the term ‘option for the poor’ has never stopped stirring up debate. In its development, the social teaching of the Church adopted the expression and even enriched it with the term ‘preferential’ at the meeting in Puebla (1979). To examine the universal appeal of the expression today, this thesis turns to two contemporary Jesuits: Jon Sobrino and Pope Francis. Sobrino is a Spaniard but has worked and continues to work as a missionary in El Salvador,in Latin America. Pope Francis is Argentinian. Before becoming Pope, he exercised his ministry in Latin America. This research made up of six chapters, compares the theological views of Sobrino and Pope Francis to show not only the complexity of the expression itself but also to demonstrate that this expression should be replaced by an alternative expression. The introductory chapter sets the scene by analysing the origin and development of the term ‘preferential option for the poor’ and its various components. It also introduces the term ‘vulnerable’ and compares it to the term ‘poor’. The second chapter examines the notion ‘poor’ in Sobrino’s Christology and theology. The poor are also called ‘victims’ or ‘crucified people’ and they are central in Sobrino's theology of salvation. For this reason, this research introduces a third chapter to analyse critically what is considered as a credoby Sobrino namely ‘Extra Pauperes, Nulla Salus,’ ‘outside the poor there is no salvation’ Chapters four and five are dedicated to Pope Francis. They offer not only the keys to interpret his theological thought but also make a critical analysis of his understanding of the poor. The last chapter deals with the comparative analysis of the language used by the two Jesuits to describe the poor. It also points out the similarities and differences. The language of mercy is the common ground in their theological views. One of the differencesbetween themis about the poor.Sobrino’s understanding of the poor focuses mostly on the economically poor while Pope Francis defines the poor in an inclusive way. He includes not only other forms of human suffering but also the sufferings of all of creation. Nevertheless, the two theological views are complementary. This harmonizing of views about the terms ‘poor’ and ‘mercy’ by Sobrino and Francis has raised questions about the use of the expression ‘preferential option for the poor’ in theology today. Considering the new forms of human suffering described by Pope Francis in today's world, this thesis proposes to replace the ‘preferential option for the poor’ with the expression ‘compassion for the vulnerable’