Al-Shamsi (الشامسي) is a very large Arabian tribe (with many sub-tribes) that mostly inhabit the northeastern part of the Arabian peninsula. They are located mainly in Oman, the United Arab Emirates, and to a lesser extent Qatar, eastern Saudi Arabia and Bahrain. Due to the large nature of the tribe, there are today in fact many branches that trace themselves to Al-Shamsi tribe.
It is presumed that Al-Shamsi tribe was the progeny of who was said to be the brother of khraiban "al-nuaimi", and in turn the father of the Al Nuaimi tribe. Therefore, there are two sections of Al Nuaimi tribe, one is Al Bu Khraiban "Al-Nuaimi" and the second is Al Bu Shamis "Al-Shamsi". Both tribes claim lineage to the Azd tribe from Yemen in around the 3rd Century AD, which immigrated from Ma'rib after the destruction of the dam. The Azd are Qahtanite Arabs and not Adnanite. 
It is widely thought that the Al-Shamsi tribe immigrated from Western Arabia to settle around the Sanina area (an inland desert area between the Southern United Arab Emirates and Oman border)or more commonly known as Al-Hamawiya region during the late 17th century. Later migrations led some of them to Al Ain / Buraimi oasis towns while other migrated eastward towards the Omani coastal areas.   The Al Shamsi also were the rulers of Hamriyah Port until the early 1960's before it fell under the rule of the Sharjah Emirate.
It is thought that Al-Shamsi is related to the following other Arabian tribes:
The following are branches of Al-Shamsi: