The development of Religious Identity in accordance with the Marcia’s Identity Model is examined based on the following three hypotheses. First, during adolescence, with increasing age and level of Religious Identity development, there is an increase in the level of Moratorium and Achievement, while on the other hand there is a decrease in Diffusion and Foreclosure. Second, in relation to Religious Identity development, there is a significant difference among Intrinsic Religious Orientation, Extrinsic Religious Orientation, and Quest Religious Orientation. Third, in Religious Identity development, for the Mature Faith Scales there is a significant difference between the Horizontal Themes and Vertical Themes. The participants of this research study were 1,872 Catholic youth, who were divided into five groups. The measurement instruments included the Religious Identity Questionnaire, Religious Orientation Scale, Mature Faith Scales, among others. Overall, the results of the research study support the three hypotheses. First, Marcia’s Identity Model was replaced with Religious Identity, and among the four identity measures, there was a tendency for Moratorium and Achievement to increase with age, while on the other hand Foreclosure and Diffusion decreased with age. Second, with regards to Allport’s Religious Orientation, Intrinsic Religious Orientation showed a significantly higher difference with Religious Identity then Extrinsic Orientation. In addition, Batson’s Intrinsic Orientation was significantly higher then Extrinsic Orientation for Religious Identity Development. Third, there was a significant difference between Religious Identity and Mature Faith. In other words, individuals with Horizontal-Theme orientation tendencies have clearer Religious Self-Identity then individuals with Vertical-Theme orientation.