We know that Christianity has been growing remarkably in recent decades—in China there is talk of “Christianity fever”. We don’t know just how many Christians there are in China at present. The reason for this is simple. Christian churches in China come in two groups: those that are registered and officially recognized by the government, and those that are unregistered, technically illegal though widely tolerated, and therefore extremely difficult to count. Most of the growth has occurred in the latter group. In a recent article in The Christian Century (the banner periodical of mainline Protestantism in America), Philip Jenkins has...