Pew Research Center polls conducted in 2011-2012 find high levels of concern about sectarian tensions in several countries where Sunnis and Shias live side by side. These concerns are particularly pronounced in Lebanon, where fully two-thirds of all Muslims, including about half of Shias and 80% of Sunnis, say sectarian tensions are a very big or moderately big problem. Roughly half of all Muslims in Iraq, more than four-in-ten in Afghanistan and nearly a quarter in Iran say the same. The polls were conducted from November 2011 to May 2012 among a total of more than 5,000 Muslims in five countries with substantial numbers of both Shias and Sunnis (Afghanistan, Azerbaijan, Iran, Iraq and Lebanon).2 Although Shias make up only about 10%-13% of the world’s Muslims, three of the five countries surveyed (Iran, Iraq and Azerbaijan) have Shia-majority populations.3 Several of the countries polled also have a recent history of sectarian violence. This includes Lebanon, where a civil war was fought along sectarian lines from 1975 to 1991, and Iraq and Afghanistan, where bombings and other suspected sectarian attacks have occurred in the last few years.