Target audience: everyone working with any agile methodology: Scrum, XP, Kanban, …
Urs’ comment: If you want to get the most out of your requirements in your agile project then this book is for you. Mike Cohn shows User Stories as the building blocks of agile requirments engineering. The book covers how to use User Stories, their advantages, their limitations and a lot of real-world project know-how around User Stories. If you work with User Stories then you should have read this book.
As a side note: skip the estimation chapter if you are going to read Agile Estimation and Planning by Mike Cohn.