This book, written in an intentionally informal style, aims to make Old Irish grammar more accessible to students of all backgrounds. The material is based on handouts that have been used by students in Old Irish grammar courses at various universities for over a decade, and comments and suggestions for improvements offered by both students and instructors have been incorporated. It can serve as a stand-alone introduction or can be used in conjunction with other grammatical works, in hopes of elucidating some of the tricky concepts that makes Old Irish such a fascinating and rewarding subject for study.