In all matters of demography in Yemen, statistics are very limited, and estimates vary immensely. One example of the confusion is with the size of the Zaydi community, estimates go from 25% to 47% of the total population.
The figures here are rough estimates, as very little background matieral exists.
All the information below is approximate, but it is based upon all the very best sources available.
Yemenis belong to one of two major branches of Islam; Sunni or Zaydi. The unification of the Yemens in the 1990's caused the Sunnis to become the majority, prior to this, the Zaydis had been the majority in North Yemen.
Coexistence between the two groups has been peaceful, but over recent years, foreign interests have brought propaganda, mainly anti-Zaydi, to the country from Saudi Arabia and Iraq. Yemeni authorities have launched measures to curb the growth of extremism, allowing only schools that teach a moderate version of Islam to operate. More than 4,500 extremist institutions have been closed down, and many individuals sent back to their home countries.
In many local communities, Zaydis and Sunnis attend the same mosque for prayer.
Yemen is today the homeland of Zaydi Islam, a branch of Islam originating in the early 8th century; 88% of the near 13 million Zaydis live in Yemen. Sources disagree to their number, some estimates set the Yemeni part of Zaydism as low as 5 to 6 million. LookLex finds good reasons to go far higher, considering the population figures of the regions where Zaydism always has dominated.
Zaydism is found in the Northern Yemen, continuing into Hadramawt, but not along the coast.
Although it is historically correct to label Zaydi Islam as Shi'ism, it must be noted that developments over centuries have brought the theologies of Zaydi and Twelver (Shi'ism of Iran and Iraq) quite apart. Still, Zaydis have a strong affinity to Twelvers, and in times of persecution, Yemen has been the country most willing to grant protection to Twelver refugees.
Zaydis are largely overrepresented in the political elite and in the military leadership.
Although Sunnis in the south and southeast have beliefs and practices within mainstream Sunni Islam, they belong to the small Shafi'i school (madhhab) of Sharia (Muslim law). Many Yemeni Sunnis are of groups that have immigrated to Yemen in recent centuries, Asians and Somalis.
Isma'ilism is by many classified as a branch of Islam, but LookLex classifies it as a unique religion.
The Isma'ilis live in the northwest of Yemen, their historical and cultural homeland continues into Saudi Arabia. Their numbers is hard to determine, some estimates go as high as 5%, but considering the size of their community in Saudi Arabia, LookLex gives an estimate of 0.3%. During periods of suppression from the Zaydis, many Isma'ilis have left for India; the Indian Buhras are of Yemeni stock.
The main centres of Isma'ilism is the town of Manakha. The most important Isma'ili sanctuary, and goal of pilgrimage, is the grave of Hatim bin Ibrahim in the Haraz mountains.
The Christians and Hindus are living along the southern coast, mainly around Aden. These are "leftovers" from the time when Yemen was an important stopover on the trade between Europe and the East. Judaism has a long history in Yemen, longer than Islam. The Jewish communities today count only a few hundred souls that did not join the migration waves to Israel.