It was from the Great Mosque in Mosul that Isis leader Abu Bakr al-Baghdadi declared a new Caliphate and himself the head of all Muslims, at which point the US formed a coalition to help Iraq defeat them.
New Zealand and Australia jointly run a training camp for Iraqi security forces, one of five across Iraq, which has prepared them to take on Isis.
In Mosul, the Iraqi military are backed up by Coalition forces in a capacity to advise and assist, and which order air strikes on Isis targets.
The United States, which has about 5000 military in Iraq, is the primary support partner but Australian forces are close to Mosul as well in an advisory role.
Australian F-18 fighter jets have conducted more than 120 strikes on targets during the battle for Mosul out of more than 450 air strikes. About 400 Australians are in the Air Task Group, about 80 are in the special operations task group (SOTG) in the advise and assist role to Iraqi military outside Mosul and about 300 are at Camp Taji with New Zealanders.
Eastern Mosul took about three months to recapture. US General Joseph Votel told Foreign Policy magazine that about 500 Iraqi forces were killed in the battle for Eastern Mosul and 3000 wounded.
Have they had other successes?
Fallujah was the first Iraqi city captured by Isis, in January 2014. Only about 70km west of Baghdad, it was recaptured by the Iraqi military in June 2016.
Tikrit was captured by Isis in June 2014 and was regained by the Iraqi military in April 2015. The hometown of former dictator Saddam Hussein, it is about 160km north of Baghdad.
Ramadi was captured by Isis in May 2015 and recaptured in December 2015. A city formerly of at least 500,000 in Anbar province, Ramadi is about 112km west of Baghdad.
What is next?
If Mosul has been the capital of Isis in Iraq, Raqqa is its base in Syria and it will be the next target after Mosul, later this year.
About 400 US Marines and Army recently entered Syria - joining 500 US who were already there - to set up an artillery outpost to support the move against Raqqa, whenever it occurs.
They are armed with 155mm artillery guns.
The US is also training local Arabs to join the Syrian Democratic Forces (SDF), an alliance of militia including the Kurdish YPG and the Syrian Arab Coalition.
Isis is also being fought by Syrian anti-government rebels fighting under the banner of the Free Syrian Army.
The Syrian Army of President Bashar al-Assad, which is supported by Russia, has complained about the Americans entering Syria but wont be attempting to remove them either because they are also fighting Isis.
