The American Academy of Ophthalmology (AAO) published the Adult Strabismus Preferred Practice Pattern(PPP) in September 2019.The PPP provides an authoritative guidance for the clinical diagnosis and treatment of adult strabismus based on the best clinical evidence.This PPP of version 2019 incorporates recent advances in the field of adult strabismus into the guide, and comprehensively describes and updates the definition, epidemiology, classification, diagnosis and treatment of adult strabismus.This article introduces and interprets the main content of the guide.