"On the Official Language of the Republic of Northern Macedonia" includes a scientifically based text on the topic of the official language of the Republic of Northern Macedonia, written in a popular language and intended for a wide range of readers, which BAS publishes in an illustrated edition. The authors are scientists from the Bulgarian Academy of Sciences and three universities - Sofia University "St. Kliment Ohridski ”, University of Veliko Tarnovo“ St. St. Cyril and Methodius ”and Southwestern University“ Neofit Rilski ”- Blagoevgrad. The book contains very precise text based on documents. It states that the official language of the Republic of Northern Macedonia is a southwestern written-regional norm of the Bulgarian language. A roadmap for bilateral relations in the scientific and cultural spheres has also been proposed.