With Saudi Arabia now firmly in the Islamic State’s crosshairs, concern over sectarian tensions in the kingdom’s volatile Eastern Province is rapidly increasing. The Islamic State has initiated a campaign of violence and terrorism targeting Saudi Shi`a to create and take advantage of worsening relations between Sunnis and Shi`a. The group has also increasingly targeted Saudi security forces. This apparent shift may represent an attempt to exact revenge against the monarchy over its role in organizing a multinational military coalition to contain and ultimately destroy it. It may also reflect the Islamic State’s growing confidence in its capacity to organize and sustain a violent campaign against the monarch. Meanwhile, the kingdom’s execution of dissident Shi`a cleric Sheikh Nimr Baqir al-Nimr in January has aggravated an already incendiary situation. Taken together, these developments portend a period of potentially unprecedented instability in the foreseeable future.