thumb|right|Yemeni Desert.The Ramlat al-Sab'atayn (Arabic: رملة السبعتين) is a desert region that corresponds with the northern deserts of modern Yemen (Al-Jawf, Marib, Shabwah governorates) and southwestern Saudi Arabia (Najran province).[1]
It comprises mainly transverse and seif dunes and covers an area of about 60by, roughly 10000sqmi.[2]
The Ramlat as Sab'atayn includes part of what was known to medieval Arab geographers as the Sayhad (Arabic: صيهد|translit=Ṣayhad). It extends from al-Khawr to the edge of the Rub' al-Khālī or Empty Quarter. It includes the Yemeni muhafazahs of al-Jawf, Ma'rib and Shabwa.