Thank you for your question because it is one that many folks would like to have answered. Divorce is a civil term which is technically not used or recognized by the church per se. A person who freely abandons their spouse through divorce can be said to commit a sin in doing so. However, this is not the same for a person who is unjustly divorced by their spouse or for someone who must separate themselves civilly due to abuse or danger from a spouse.
Concerning “annulments,” the church has a language problem in that church tribunals grant declarations of nullity, meaning that a marriage was null from the beginning either due to an impediment or defective consent; the term “annulments” is improper (even though its commonly used by people in the church) because annulments are not granted because no earthly power can undo a valid marriage. In rare occurrences, the Roman Pontiff (the pope) can decree the dissolution of a non-consummated marriage since a marriage is not indissoluble unless it is consummated.
Like anyone, as long as one is in the state of grace, a person who is divorced but not remarried is free to approach the sacraments. Canon law requires a Catholic who is divorced to have their previous marriage examined by a tribunal and be declared free to marry before entering into a new marriage. The same is true for a Catholic who wishes to marry a non-Catholic who was previously married, be they a Christian, any other religion, philosophy, or no religion at all; the previous marriage of the non-Catholic must be examined by a tribunal and they be declared free to marry the intended Catholic spouse.
Father Chris House is rector of Cathedral of the Immaculate Conception in Springfield, chancellor, and vicar judicial and director of the Department for Canonical and Pastoral Services at the Diocese of Springfield in Illinois.