I have been following Jonathan Birch and assigning his articles to students for years and I was hence thrilled to learn about this book. This book puts together some of his key ideas in an engaging, accessible and still philosophically stimulating way. "PART I: The Zone of Reasonable Disagreement" is a great summary of many philosophical ideas on the topic of sentience, often more accessible than the original texts it discusses. For instance, the IIT is displayed clearly and compellingly. This is the part that will be interesting for all philosophers and students of philosophy, even if they don't care about animal sentience (which they should). "PART II: A Precautionary Framework" introduces the ethical foundations of the book, in a way that carefully avoids invoking the principle of charity too broadly (otherwise we could end up not taking antibiotics because we have not definitely established that bacteria are insentient). "PART III: Sentience and the Human Brain" does not only discuss embryos, but also neural organoids and the limits of sentience in human beings. Some of its topics were completely new to me (neural organoids), but even the ones I had read extensively about (such as the debate about the chronological debates on the beginning and end of life) got new life through Birch's treatment. "PART IV: Sentience in Other Animals" is the part I was mostly looking forward to. Birch is possibly more cautious than I would have, and his arguments are therefore careful and compelling, establishing at each step a zone of reasonable disagreement where different opinions can co-exist and which can be hard to resist, even for people in favour of the intensive use of animal farming etc. "PART V: Preparing for Artificial Sentience" is the part I was least looking forward to, because debates on AI often focus on LLMs and seem to me to be a distraction with regard to the incumbent problem of caring for sentient beings all around us, especially non-human animals. However, again Birch discusses well known topics (like LLMs) in a fresh way, and is also able to propose examples that shake one's (surely mine) deep seated convictions. In short, an absolute must for all philosophers, ethicists, people interested in animals and/or AI and for everyone looking about new ways to think about the world. Jonathan Birch never shouts, but his arguments are therefore all the more clever and convincing.