Recent New Zealand demographic data has indicated a continuing trend towards secularisation in this country, with more individuals unaffiliated with any religious organisations than ever before. Nevertheless, approximately 49% of New Zealanders still identify with a Christian faith (including Catholic, traditional and non-traditional protestant denominations), and a growing minority (3.5%) identify with one of the other major religions (e.g., Islam, Hinduism, Sikhism; Statistics New Zealand, 2014). In spite of this large proportion of New Zealanders that profess some type of religious affiliation and a strong history of religious beliefs for both Māori and New Zealand Europeans, there has been very little research from New Zealand regarding the development of spirituality and religiosity in young people. The aim of this study was to explore this question in a group of 87 religiously affiliated young people (aged 16-21) and a subsample of 12 interview participants through an embedded mixed methods study. The research questions examined the distinctions between “religiosity” and “spirituality”, the factors that young adults perceive as influencing the development of their faith identity and spirituality, and the associations between faith identity, religiosity and spirituality, religious motivation, social connectedness, demographic factors, and three indicators of mental health (psychological well-being, anxiety, and depression). The quantitative analyses showed that faith identities characterised by higher diffusion (disengagement with faith) and moratorium (exploration/doubt) predicted lower spirituality and religiosity; whilst intrinsic reasons for church attendance predicted higher spirituality and religiosity. Levels of psychological well-being and anxiety were predicted by spirituality (but not religiosity), moratorium faith identity, and relational quality with parents and peers. The negative association between spirituality and anxiety was mediated by higher moratorium faith identity. Finally, symptoms of depression were only predicted by relational quality with parents and peers, and connectedness to community. The qualitative analyses revealed that spirituality and religiosity were considered to be different concepts, distinguished by associations with the individual and the institution respectively. The interview participants believed their spiritual development to be largely influenced by their parents and mentors, interacting with their church community and participating in church activities more frequently than just Sundays, as well as having a personal connection to God. The results revealed contrasts between the two types of analyses, whereby higher questioning and exploration was associated with lower spirituality in the quantitative analyses, but in the interviews, the young people believed questioning faith to be a positive influence on spiritual development. These findings are discussed from the perspectives of identity development, stages of faith development, as well as in terms of the methodology of the study. Further, the associations between mental health and social connectedness add to the discussion whereby the impact of moratorium on spirituality and mental health may be influenced by the social environments and church settings in which young people practice their faith and spirituality.