Caliph Abū Bakr is the most crucial figure in the history of Islam during and after the Prophet's era. He was the first caliph in the history of Islam. He performed essential services in Islam's invitation, notification, and guidance. He ensured peace in society by successfully managing the problematic process that emerged after the death of the Prophet. The subject of this communiqué is the letters of invitation to Islam written during the reign of Abū Bakr. While most of these letters were written by Abū Bakr, some were by Khalid b. Walid, was the most important commander of this period. There are more than fifty such political, military, and diplomatic letters. Abu Bakr had a significant role in forming the Islamic society and establishing Islam in the community, starting from the Prophet's era. Among the first Muslims, there are dozens of personalities whom he was instrumental in converting to Islam. After the Prophet's death, his efforts like invitation, communiqué, and guidance, especially in establishing peace in the society and initiating the conquest movements, express the value of his efforts like invitation, communiqué, and guidance. Addressing the role of Abū Bakr's period in preaching Islam will contribute to a better evaluation and understanding of this period in Islamic history. This study focuses on the letters of invitation to Islam written during the reign of Abū Bakr. To shed light on our study, the subject has been investigated through qualitative research and literature review method by examining the early Islamic history sources, including the period of Abū Bakr, especially the work entitled Jamharat al-Rasail al-Arab and Tārīkh al-Ṭabarī, in which these letters were compiled, as well as research books, articles, and theses written on the subject today. During his caliphate, Abū Bakr was a man of preaching and enlightenment. His personal life, his stance as a statesman, the effective methods he applied for the Islamic invitation, notification, and guidance, and his decisions made it possible for Islam to be recognized and spread in the right way and for the peace of the people. Abū Bakr used different methods related to the invitation to Islam in his activities. As one of these methods, he invited people to the truth through letters, warned them about their mistakes, and tried to preserve the line of Prophet Muhammad by reminding them of forgotten facts. Sometimes he achieved his goal by paving the way for more efficient communication through mutual correspondence. In the letters he sent to the commanders during his caliphate, he guided them in terms of military strategy and advised them to be spiritually strong. He first communicated Islam to the apostate tribes, and those who turned away from Islam were informed that they would be dealt with accordingly. He also sent letters to his governors and zakat officials, reminding them of their duties and advising them to preserve Islamic sensitivities. With these efforts, he calmed the chaotic environment that emerged after the Prophet, ensured the unity of Muslims, and eliminated the obstacles to the spread of Islam.