This book is indispensable for students of poetry. Saintsbury's 3-volume history of English prosody is a beast (being 3 volumes), and this single-volume distillation is handy, incredibly readable, and carries a useful glossary of prosodic terms at the end. Students of contemporary (or at least post-1900) poetry will want to supplement it with a more current volume to deal with the post-Ezra Pound breakthroughs (or breakdowns, depending on your stance), but this is as good a foundation as you can get.