It is a comprehensive (really) book - ITIL4 Foundation Complete certification kit by Scott Tunn really helps you to understand the topic
Johnny HuAlabama
I suppose ITIL4 Foundation Complete certification kit is a super informative and insighful - Scott Tunn explained all the details in a perfect manner
Steph D. RitzPasadena
I found this book very helpful - Scott Tunn is a great teacher and writer. Probably ITIL4 Foundation Complete certification kit is the one of the best on the topic