The authors of CanonLaw.info have collected some resources for the understanding of Canon 915, which states: ‘Those who have been excommunicated or interdicted after the imposition or declaration of the penalty and others obstinately persevering in manifest grave sin are not to be admitted to holy communion’.
The reason for the attention to this text by the American website is in the first place the discussion about whether or not politicians who support, for example, abortion, should be admitted to Communion. It’s an issue that is very much alive in the Church in the United States, but many of the arguments and explanations also apply to other people who can’t or shouldn’t receive Communion. The Code of Canon Law talks about ‘grave sin’ in Canon 915, and doesn’t distinguish between the various sins there.
A very interesting and detailed resource.