The book demon­s­t­rates that ʿAmmār al-Baṣrī’s Kitāb al-Masā’il wa-l-ajwiba is an signi­fi­cant piece of Chris­tian theo­logy that played an important role in the trans­mis­sion of Greek wisdom and Helle­nistic know­ledge to Muslim theo­logy. On the basis of various Arab Chris­tian and sources and their termi­no­lo­gies, the book exhi­bits that the Chris­tian authors of the ninth century had already had a ready set of termi­no­logy in Arabic. The study proves that the termi­no­logy of the Kitāb al-Masā’il wa-l-ajwiba corres­ponds to Greek philo­so­phical termi­no­logy, more speci­fi­cally in the form these terms were used by Church Fathers in Patristic lite­ra­ture. Through repre­sen­ta­tive exam­ples: the concept of the intel­lect, referred to by the term ʿaql; terms deno­ting the body and incar­na­tion; terms refer­ring to eternity or perpe­tuity, conti­nuity; terms deno­ting crea­tion; terms of father­hood and sonship; and terms refer­ring to unity, unifi­ca­tion and union, the compa­ra­tive termi­no­lo­gical exami­na­tion inclu­ding contem­porary and later Muslim sources also shows that in some cases Chris­tian authors influ­enced the forma­tion of Muslim termi­no­logy, while in others both parties relied on a shared tradi­tion, or mutually known sources.