阿拉伯人进攻叙利亚始于629年，时伊斯兰教先知穆罕默德尚在。宰德·伊本·哈列赛（穆罕默德的义子）率三千人于摩耳台（死海南端的东面）袭击东罗马军队，战败，宰德阵亡。这也是穆斯林对基督教地区的第一次战争。
632年，穆罕默德去世。6月8日，艾卜·伯克尔继任，号哈里发。633年秋，遣三支军队，以阿慕尔为总司令，攻叙利亚。634年，败巴勒斯坦的罗马贵族塞基阿斯。2月4日，歼灭罗马溃兵于达辛。此后哈里发艾卜·伯克尔令哈立德·伊本·韦立德增援。3月，哈立德从伊拉克边境刚征服的希拉城出发，急行军十八天，至大马士革。其中五天行于沙漠，以皮袋贮军队饮水，沿途宰驼供膳，以驼胃之水饮马。军士五百至八百人，乘驼，而备战之马空骑与驼并驰。会师后哈立德任联军最高指挥。7月30日，败罗马于艾只那代。635年9月，围攻大马士革六个月后，降之。大马士革投降的条约也成为以后各城投降阿拉伯人的范本，规定：阿拉伯统帅进城后答应保护居民的生命、财产和教堂，城墙不被拆除，任何穆斯林不驻扎在他们的房屋里；居民需要缴纳人丁税：每人每年交一个第纳尔和一袋小麦（在第二位哈里发欧麦尔时代有所增加）。其后叙利亚诸城相继陷落。
此时，东罗马皇帝希拉克略集结了五万多人，以其弟西奥多拉斯为帅，抵御阿拉伯人。哈立德暂弃霍姆斯、大马士革诸城，于约旦河左岸雅穆克河谷集二万五千余人与罗马军队作战。636年8月20日，天大热，大败东罗马军队，杀西奥多拉斯。希拉克略逃回。叙利亚遂归属阿拉伯。
639年，阿慕尔开始进军埃及。640年7月，在阿因·舍木斯城击溃东罗马军队。642年9月，埃及首府亚历山大港降，东罗马军队撤退。而阿慕尔在巴比伦堡外的营地建成新都弗斯塔德（开罗）。埃及成为阿拉伯帝国的重要财政来源。
645年底，亚历山大港人乞兵于东罗马，君士坦斯皇帝派遣船三百艘收复亚历山大港。而刚去职的阿慕尔得到复职，在尼丘击败东罗马军队，646年初，重新占领亚历山大港。649年，叙利亚长官穆阿威叶夺取塞浦路斯岛。
In 639 an army of some 4,000 men was sent against Egypt by the second caliph, Umar, under the command of Amr ibn al-As. This army was joined by another 5,000 men in 640 and defeated a Byzantine army at the battle of Heliopolis. Amr next proceeded in the direction of Alexandria, which was surrendered to him by a treaty signed on November 8, 641.
Alexandria was regained for the Byzantine Empire in 645 but was retaken by Amr in 646. In 654 an invasion fleet sent by Constans II was repulsed. From that time no serious effort was made by the Byzantines to regain possession of the country.
In return for a tribute of money and food for the troops of occupation, the Christian inhabitants of Egypt were excused military service and left free in the observance of their religion and the administration of their affairs.
Conversions of Copts to Islam were at first rare, and the old system of taxation was maintained for the greater part of the first Islamic century. The old division of the country into districts (nomoi) was maintained, and to the inhabitants of these districts demands were directly addressed by the governor of Egypt, while the head of the community—ordinarily a Copt but in some cases a Muslim Egyptian—was responsible for compliance with the demand.
The resentment of the Copts against taxation, however, led to a revolt in 725. In 727, to strengthen Arab representation, a colony of 3,000 Arabs was set up near Bilbeis. Meanwhile, the employment of the Arabic language had been steadily gaining ground, and in 706 it was made the official language of the government. Egyptian Arabic, the modern language of Egypt, began to form. Other revolts of the Copts are recorded for the years 739 and 750, the last year of Umayyad domination. The outbreaks in all cases are attributed to increased taxation.
The Abbasid period was marked by new taxations, and the Copts revolted again in the fourth year of Abbasid rule. At the beginning of the 9th century the practice of ruling Egypt through a governor was resumed under Abdallah bin Tahir, who decided to reside at Baghdad, sending a deputy to Egypt to govern for him. In 828 another Egyptian revolt broke out. And in 831 the Copts joined with native Muslims against the government.
In the 9th century Egypt was mostly governed by Turks (Tulunids, Ikhshidids) ruling in the name of the Muslim governor. Egypt came into conflict with Syria and the Caliphate until peace was made in 891. In 914 Egypt was invaded for the first time by a Fatimid force sent by the Caliph al-Mahdi Obaidallah, now established at Kairawan. The Mahdi's son succeeded in taking Alexandria in 919, and Egypt wasn't freed from the invaders until the year 921, when reinforcements had been repeatedly sent from Baghdad to deal with them. In 969 the Fatimid general Jawhar as-Siqilli was placed at the head of an army said to number 100,000 men and attempted to seize Egypt. He had little difficulty defeating the Egyptian army. And on July 6, 969, he entered Fostat at the head of his forces. Egypt was transferred from the Eastern to the Western caliphate.