This paper reports the preliminary findings of a qualitative investigation into the experience of genetic paternity testing. It provides a typology of the main situations where paternity is contested through the use of genetic testing; that is, why and to whom paternity testing matters. Paternity has generally been accepted as a taken for granted state that defined the relationship between a child born within an established partnership and the male partner. The development of a cheap, efficient and commercially available genetic test for accurately detirmining biological paternity changed this reliance on presumed paternity. Initially a tool of the State to enforce paternal responsibility, it has more recently become a faciliative mechanism for men to know with absolute certainty about their paternity or non-paternity. The main situations in which testing is used involve men and women caught up in relationship breakdown and contestation over paternity and Child Support. Paternity testing is sought either by the man to terminate parental responsibility or by the woman to ensure it. These complex situations are reported from the perspective of both men and women. The paper then discusses some of the key social issues regarding the use of this new technology and argues that its availability and use matters to all of us.