Catholic canon law changes very slowly, but it constantly adds rules, interpretations, and applications. Some canons are frequently invoked, and others rarely used, quietly pass from memory. In the dozen or so years since this introduction to canon law was first written, there have been many changes and adaptations. This is one reason for a revised edition, although many of the alterations are too subtle to be captured in an introductory treatment. A second reason is to include some of the many new resources, commentaries, and explanations which authorities in the field have made available. Since many have found the original book helpful in beginning their exploration of the church's regulations, a fact which gratifies its author greatly, it is worth improving. Hence many sections have been clarified, expanded, and updated, and some others deleted. In a few places the material is reordered. Seven new case studies have been added. These improvements are a third reason for revision.