Two famous stimulants, coffee (Coffea arabica) and qat (Catha edulis), arrived to Yemen from East Africa at about the same time, probably during Yemen’s Rasulid era. Although there is a substantial literature on both of these plants in Yemen, there is still confusion about how and when they were introduced to Yemen. This paper examines the historical literature, literary texts, lexicons and folklore to piece together the various theories about the arrival of both plants into Yemen. Coffee probably spread to Yemen by the mid 1400s and became important enough for a conference on its prohibition to be held in Mecca in 1511. Yemen became an exporter of coffee beans, reflected in the use of the term “Mocha” to refer to coffee due its export from the Res Sea port of Mocha. Qat may have arrived as early as the 14th century during the reign of al-Malik al-Mu’ayyad Dawud, but thus far no reference to qat or coffee has been found in any surviving text from the Rasulid era. Based on the information in Ibn Fadl Allah al-Umari’s (d. 1349) Masalik al-absar fi mamalik al-amsar, it is clear that the Arabic term is derived from the Amharic. In this paper I trace how the term was transformed in Yemeni dialects. There was considerable debate about the legality of both coffee and qat, including a small treatise by Ibn Hajar in his fatawa collection. Yemeni poets also waxed eloquent about both stimulants. This paper will update the information on qat in both editions of the Encyclopedia of Islam and earlier references.