The Private Letters of Baginda Omar (1839 - 1876) held by the National Archives Malaysia constitutes one of the most important accessible primary sources of historical information available on the socio-political and economic development of Terengganu Darul Iman in the 19th and early 20th centuries. Inscribed as the fifteenth tangible heritage object in the National Heritage Department of Malaysia's National Heritage List, these royal letters have been preserved, in various forms, by the National Archives' headquarters in Kuala Lumpur since 1960. This study is the first comprehensive attempt at rationalising the complexity of this challenging collection, by presenting its principal material in a systematic and coherent manner. This publication has been divided into two parts. Volume I provide an introduction to the collection and its main subject, with a critical transliteration and annotated translation of the original Malay-Jawi documents. Volume 2 offers a descriptive catalogue to the collection, plus a diplomatic transliteration of the Malay-Jawi letters. It is hoped that this preliminary examination of the letters will provide the basis and impetus for further studies to be made of the collection.