Backed by the US-led coalition, the Iraqi army is advancing towards the country's second-largest city, where an estimated one million civilians are trapped.
Roughly 4,500 IS fighters remain in Mosul, while coalition forces number 30,000.
While IS sniper fire and booby traps have slowed the government forces, they remain greatly outnumbered.
IS lacks central policy
It remains to be seen whether fighters will take advantage of the humanitarian corridor opened to the west of the city for fleeing civilians.
So far roughly 900 people have fled Mosul by way of this corridor.
IS leader Abu Bakr al-Baghdadi has yet to announce his strategy for the Mosul campaign.
Al-Baghdadi could either stand and fight for Mosul or order his fighters flee to Syria, says Hazhir Teimourian, former Middle East columnist for the London Times.
"If he decides that he must make a stand and fight in Mosul, because it is so strategically and symbolically important, then he will try to prevent his fighters from fleeing the city," he comments.
"On the other hand, if he decides to save his fighters for a greater fight in Syria, where he's also under attack, then it's quite possible that he will order them to retreat quickly while this corridor still exists."
What does this battle mean for IS?
Losing Mosul will be a considerable set back for al-Baghdadi and his forces.
But, according to Wassim Nasr, a journalist at France 24, it does not signify the demise of the group.
"They already went underground and proved that they can emerge and come back stronger."
He notes that the "objective elements" that gave rise to IS still exist: "popular support, political instability, a failed state, a very bad economic situation and a very bad educational situation."
Despite military pressure and million of dollars spent on offensives, Nasr believes that IS "will pop up again".
Peter Leah, a lecturer in terrorism studies at the University of St Andrews, says it is "very unlikely" that peace will be restored after the offensive.
He predicts that "bloodshed will go on for a long time" as corruption and partisanship will block "the possibility of a peaceful solution to this conflict".
"It's a zero-sum game," is his judgement.
The campaign is expected to take many months.