The present study's objective is to analyze the phenomenon of the mustabsirūn in Twelver Shī'ism in modern times. The term mustabsir is used among (Twelver) Shī'ites to refer to someone who has left his previous faith, converted to Shī'ism and adopted its doctrines. In this study we inquire into the meaning of the term in general, in the Qur'ān and its commentaries, and as a specific term. We examine the motivation for conversion to Shī'ism, the types and status of converts and the reasons which drive them to convert, the pressures and threats which converts face from Sunnī circles and how converts cope with these and respond to the attacks on them. The study also surveys mustabsir websites and their contents, books which such converts have written, describing their conversion experience, as well as factors which have contributed to the popularity of the conversion movement, among them the support which Iranian cultural missions provide to converts, the Lebanon War of 2006 and the burgeoning popularity of Hasan Nasr Allāh, the political protection which many converts enjoy, monetary and economic emoluments given to converts, and Shī'ite satellite TV stations and websites. The study's main conclusion is that the terms mustabsir ("he who has had his eyes opened", convert to Twelver Shī'ism) and istibsār (the verbal noun: conversion) have taken on a clear and definite meaning, denoting a real trend in recent years, although still relatively limited in scope, so that at present and in the foreseeable future Sunnī Muslims have no reason to fear this trend.