The Jaysh al-Mahdi (Mahdi Army) is the militia of Muqtada al-Sadr, a major Shi'a political figure in Iraq. Jaysh al-Mahdi, commonly referred to by its acronym, JAM, first became prominent in April 2004 when it fought against US forces in East Baghdad and in Najaf. In addition to fighting US and coalition forces, JAM has actively contested control of Baghdad - engaging in a long-running territorial struggle with al-Qaeda in Iraq (AQI) and other Sunni groups for control of the city. It has been held responsible for much of the sectarian cleansing in the Sunni neighborhoods in 2005 and 2006. JAM also effectively infiltrated units of the Iraqi Security Forces (ISF) during this period, including both the Iraqi Army and the National Police.

In August 2007, Muqtada al-Sadr ordered the Jaysh al-Mahdi to "freeze operations" following an outbreak of violence in Karbala, revealing that significant elements of the movement were no longer under his control. These elements, known as "rogue JAM" or "Special Groups," have continued to carry out extra-judicial killings targeting Sunni civilians, kidnapping operations, and other criminal activities. These criminal elements have continued to be the target of operations by coalition forces. There is also evidence that these Special Groups have received support from Iran.

In February 2008, Sadr extended his cease fire for six months. Despite that extension, violence erupted throughout southern Iran in late March 2008. More information on that violence and its significance is available here.