It's reminiscent of a black-and-white pirate flag and, for some, it conjures up similar feelings of death, destruction, outlaws and violence. Here is our quick explanation of the symbolism of the flag and the meaning of its Arabic phrases.
The idea of a caliphate has a powerful history for Muslims, who enjoyed their greatest political and military successes under ancient caliphs. But Muslims are divided over whether the caliphate proclaimed by ISIS militants is worthy of that proud mantle.
Over 600 people including ISIS fighters and their families were escorted from the Lebanon border by Syrian government forces. That angered the US, which launched airstrikes to block their path to a town near Iraq.
Iranian American journalist and writer Azadeh Moaveni spoke with Marco Werman about why the term "ISIS brides" is problematic and shares her perspective on the much bigger role that women have had in militant Islamic groups.