Move by Patty Azzarello
A really great book on executing strategic change, that has a section about setting ‘Control Points’, which are roughly equivalent to what Intel/Google etc. refer to as ‘Key Results’. I keep coming back to this book.
Radical Focus by Christina Wodtke
A light read about OKRs. Good as a first book on OKRs, but not as detailed as the two books above.
Introduction to OKRs by Christina Wodtke
A very short book on OKRs. Good as a first book on OKRs if you have a very very short attention span.