"Vulnerability" is a complex concept. It refers to the possibility of harm, to limitations and to the mortal condition of the human being. Nevertheless, it has different dimensions. There are at least two: an anthropological dimension, which affirms the intrinsically vulnerable condition of the human being; and a social dimension, which refers to an increased susceptibility caused by the natural environment or social settings, generating "vulnerability spaces" and "vulnerable populations". The social dimension leads us to comment on capacities and recognition as key elements of the bond amongst human beings, the ground of moral obligation. This obligation is principally care and solidarity in the framework of justice.