Summary: The issue of sexual advances by Roman Catholic priests and religious brothers towards minors, most of whom have been pubescent boys, is increasingly at the center of often heated and anguished discussion in and around the Church nowadays. There have already been far reaching consequences to the intense preoccupation with this matter. Throughout these tumultuous goingson, the term "pedophilia" is being bandied about as a catch-all name for the panoply of abuses. Semantic precision may not, of course, be the most important element in organizing to meet the horrendous challenges facing the Church in this context, but it does have its own importance. In part I of this two-part article the author expounds on the precise meaning of the terms being used. After some basic background information on human sexuality and sexual (gender and age) orientations the author will explain precisely what "pedophilia" is and who is a "pedophile" and what the medical and behavioral sciences have to say that is relevant. Part II, which will appear in the next edition of Antonianum, will address whether men who are homosexualo, especially in the priesthood and religious life, are particularly prone and pedophilia. Is this implication correct? Or is the association better understood as semantic confusion, homophobia, or both? On these and some other issues related to harm reduction and prevention, which will conclude Part II, the author aims to present the "best knowledge" among professionals today, including the author's own work, as his contribution to the ongoing discussion.