Alamiyyah refers to the concept of following the most learned jurist. General consensus amongst scholars of the Usuli school of thought is that it is an obligation for a lay person to do Taqleed of the most learned of the Shi’ite jurists, who is known as the a’lam. Below is a short extract from an essay titled The Established of the Position fo Marja’iyyt-i Taqlid in the Twelver-Shi’i Community by Ahmad Kazemi Moussavi where he discusses this specific concept and how it was formalized over time. The essay was published in 1985, in Volume XVIII of the Iranian Studies publication (I believe it also goes by the name Iran Nameh).
The concept that the jurist (whose pronouncements set binding patterns for regular mukallafs) must be the most learned mujtahid has developed within the Usuli context of the nineteenth-century Twelver-Shi’i community. It provided one of the most necessary bases for the official hierarchy of religious leadership. The notion of “the most learned mujtahid” does not appear in juridical works in the early phases of Ithna-ashari development. However, the roots of such a concept can be found in certain classical Islamic principles: for example, an Imam must be superior and the most learned person. this is true because, according to reason, a more knowledgeable person is generally preferred over a less knowledgeable one (tarjih al-fadhil ala’l-maf-dhul). This issue first appeared in early Islamic scholastic theology (Ilm al-kalaam). Twelver Shi’i jurists of the Mongol period justified the Shi’i Imam’ unique position by using this principles. According to Qazi Nurullah Shushtari’s (d. 1019/1610) definition, the Imam’s superiority should be evident in terms of knowledge, piety, and bravery.
Two centuries later, the jurists of the Qajar period, after having established the principle of taqleed in its broad sense, started to accept the marj’i taqleed as being of the same superior level of knowledge (‘ilm) as the Imam. The term a’lam, as referring to the Shi’i ulama, first appeared in Ma’alim al-Usul by Amili. But he seems essentially to have been concerned with the quality of being more precise in reporting traditions. However, the way in which Shaykh Ansari (d. 1281-/1864) was accepted as the Most Learned mujtahid at the death of Shaykh Najafi Isfahani (d. 1266/1849) shows us that the idea of the mujtahid being the most learned scholar, in its full sense, was already established. Moreover, Shaykh Ansari claimed ijma’ on the necessity of emulating the most learned mujtahid. In the late nineteenth century we find that Ayatullah Tabataba’i Yazdi (d. 1338/1920) clearly defined the principle of a’lamiyyat. According to Ayatullah Yazdi, it is obligatory to follow the most learned mujtahid of the time. The most learned mujtahid (a’lam) is he who is most informed about the rules and sources of jurisprudence and is most capable of deducing religious ordinances.
In addition to stating the doctrine of a’lamiyyat, Ayatullah Yazdi also introduced the obligatory nature of taqleed, and he concluded that any religious performance by a mukallaf without the guidance of a mujtahid is unacceptable. It must be stated that such an emphasis on the principle of taqleed is peculiar to the Qajar period. The obligation of taqleed al-mujtahid (to find a mujtahid in order to follow his directions) was presented to Twelver Shi’ism by prominent jurists of the Mongol period such as Ibn al-Mutahhar and Shahid ath-Thani. The one who elaborated on this issue, however is Shaykh Hasan ‘Amili.
 Consult Murtaza Jaza’iri, “Taqlid A’lam ya Shura-yi,”Maja’iyyat va Ruhaniyyat, pp. 216-231.
 Consult the following sources: Ibn al-Mutahhar al-Hilli, Kashf al-Murad (Mashhad: Muhammadiyya, n.d.), p.240; Nasir ad-Din Tusi, Talkhis al-Muhassal (Tehran, 1980), ed. A. Nuri, p. 206; Fadil Miqdad Suyuri, Kitab al-Nafi Fi Sharh Bab al-Hadi-‘ashar (Tehran: Mustafavi, 1979), p.66.
 Nurullah Shushtari, Ihqaq al-Haqq (Tehran: Islamiyya, n.d.), Vol. II, p, 319.
 See A. Naraqi, Manahij al-Ahkam (Tab’i Mahalli, 1896), pp. 275-7.
 See Hasan ‘Amili, Ma’alim al-Usul (Tehran: Shafi’i, 1959), p. 435.
 Murtaza Ansari, Zandiqi-yi Shaykh-i Ansari (Ahvaz: Ittihad, 1969), pp. 72-5.
 Shaykh Murtaza Ansari, al-Ijtihad wat-Taqlid (Egypt: Bulaq), p. 35.
 Muhammad Kazim Tabtaba’i Yazdi, Urwat al-Wuthqa (Tehran: Dar al-Kutub al-Islamiyya, n.d.), p. 4.