This publication is devoted to the study of a collection of Mongolian manuscripts written on birch bark, which was found in 1970 inside a stupa in the ruined city of Xarbuxyn Balgas in Northern Mongolia. The manuscripts date back to the 1st part of the 17th century. The book contains the first part of the manuscripts edited in facsimile and in Latin transcription together with detailed commentaries on the palaeographic, orthographic and lexical peculiarities of the texts. Every effort was made to identify the texts, in most cases successfully. The collection of Xarbuxyn Balgas consists of Buddhist and popular religious ritual texts which cover a vast range of subjects, such as invocations to deities, wedding calendars and prayers recited to guide the dead between death and rebirth. The collection provides the hitherto earliest available evidence of a number of texts, including texts which were previously unknown.