The research is focused on Vatican documents forming the doctrinal Catholic teaching on LGB persons in the years 1975-2005 and its unacknowledged psychological content. Identifying statements of psychological nature in these documents and confronting those statements with the wide-ranging academic research on LGB persons will serve establishing what psychological concepts, theories and beliefs underlay this church teaching. The author intends to look for a variety of topics with which these documents may be loaded, such as: personal maturity, emotional and social stability, mental health, ability to form responsible relationships, ability for parenthood etc., as well as to identify non-explicit convictions on irreversibility of sexual orientation, identity versus preference question or the importance of integrating one's sexual orientation in the process of development. The aim is to question the assertion that Vatican upheld a science-neutral stance in the doctrinal documents on LGB persons. The thesis will argue that holding such neutral stance is impossible and it results in introducing psychology to Vatican documents in non-methodological manner, possibly compromising their standards. There is a need, therefore, for a new, systematic and informed attitude towards psychological research on sexual orientation. Since there has been a growing recognition in the Vatican of the importance of engaging with sciences in the process of developing church teaching, this research hopes to contribute to that new interdisciplinary approach by proposing a new, constructive way of such engagement with the academic research on sexual orientation while taking into account its limitations, biases and changing frameworks. The doctoral research is now in its initial stages, devoted to identifying sources and the scope of its psychological content.