While both Regnum Christi and Opus Dei are lay Catholic organizations focused on spiritual growth and formation, they differ in their structures and areas of emphasis. Regnum Christi is centered around the Legionaries of Christ, while Opus Dei is centered around the personal prelature of the Holy See. Additionally, Regnum Christi places a greater emphasis on evangelization and outreach, while Opus Dei focuses more on personal holiness and sanctification.