Unlike contention based on material claims, which is overt and at times disruptive, religious resistance in post-1990s China has generally taken subtle and non-disruptive forms. Resistance among unregistered Protestants and underground Catholics, more particularly, has translated into clerics’ attempts to distance themselves from the central government’s policy of cooptation requiring legal worshipping locations to be monitored by state-led religious associations. Informality is the main channel through which groups resisting cooptation have operated. Yet underground Catholics and unregistered Protestants are informal for different reasons. For Protestants, informality commonly results from the political conviction that church and state are separate. It can also be a denominational choice or a convenient alternative to perceived burdens related to registration. For Catholics, at least historically, being underground has been intrinsically linked to deep-rooted beliefs that religious allegiance transcends political loyalty, and believers’ primary allegiance is to the Vatican rather than the Communist Party of China (CCP). Informality has had mixed socio-economic and political implications for underground Catholics and unregistered Protestant churches: unregistered Protestant churches are more socio-economically diverse and less coerced than underground Catholic churches. Finally, how underground Catholics and unregistered Protestants relate to their own informal status varies. While informality is a central part of some underground Catholics’ identity, the same cannot be said of unregistered Protestants.