This program teaches the use of the natural fertility cycle of the human body allowing married couples to know when the fertile and infertile times are to plan family size without the use of artificial contraceptives. In an effort to give practical help to married and engaged couples to live out the teachings of the Catholic Church regarding birth regulation and to strengthen the marriage relationship, a series of classes on natural family planning is taught by the Couple-to-Couple League. The League (CCL) is an international, interfaith, non-profit organization dedicated to teaching natural family planning (NFP) to married and engaged couples.