In the brutal months that followed, Iraq's second-largest city transformed into a wasteland. Buildings collapsed, residents fled and many innocent lives perished.
In addition to the humanitarian crisis taking place, an economic crisis also loomed.
Many shops under the terror group's new laws were deemed beyond the pale. Liquor stores, barbers and even toy shops were closed down.
Others were shelled to pieces.
Then in October 2016, Iraqi Prime Minister Haider al-Abadi announced the mission to retake the key city. For the next 9 months, the battle for Mosul raged.
In July this year, al-Abadi declared Mosul free from ISIS.
As Iraqis celebrated, many shopkeepers began reopening their stores.
CNN spoke to shop owners who are back in business about their experiences during and after the ISIS occupation.
Dakheel Amir -- liquor
When ISIS captured Mosul, Dakheel Amir, aged 37, says he fled 45 kilometers north of the city to his birthplace, Shekhan District, and left his liquor store behind. Selling or consuming liquor under ISIS rule was illegal.
Before the city fell, Amir says beer, whiskey, vodka and the Levantine spirit, arak, were his best sellers. Although the majority of people in Mosul are Sunni Muslim, who don't consume alcohol, there are also large communities of Christians and Yazidis, such as Amir, who do.
After Mosul was recaptured, Amir returned to rebuild a tiny new shop, his old one having burned down, in the western part of the city.
"The sales figures are high and maybe even better than they ever were before," he says. "But there is always a sense of fear from the unknown."
As such, he has installed an iron gate at the front of the shop to protect himself from an attack. Even though the city has been liberated, he says he will always remain fearful. He didn't want his store photographed for this article for security reasons.
Abdullah Risan -- women's clothing
Trying to run a women's clothing store under ISIS was difficult, to say the least, admits Abdullah Risan, aged 40.
"Most of the clothes we sold were considered forbidden during the terrorist era," he says. "Except for Islamic fashion, which is nothing more than a mere black cloth."
He used to sell women's underwear, dresses, skirts and jeans. But once ISIS took over, Risan had to dispose of his stock.
The group only permitted him to sell clothing that covered a woman's entire body from head to toe, including hands and feet. The garments had to be plain black without any inscriptions, he says.
It was even forbidden for Risan to use mannequins to display his clothes. And during some periods, men were prevented from selling women's underwear -- these items became limited to shops run by women, which men could not enter.
Risan says his store, located in the popular shopping area of Nabi Yunus market, is now flourishing.
"Today, life has gone back to normal in many ways," he says. "We offer whatever we want publicly without fear."
Sarmad Habib -- CDs
Sarmad Habib, aged 32, had only just started selling music and movie CDs when ISIS entered Mosul.
Once the city was captured, the terror group declared music and singing forbidden, saying the sounds represented forms of summoning the devil.
Instead of shutting his store down, Habib transformed it into a cafe. ISIS attacks, however, eventually reduced it to rubble.
Although at that point, it seemed to Habib that he had lost everything, right now he is hopeful.
"With the liberation of the city, I was able to re-open my CD shop with the latest music," he says. "Now I sell the most modern and distinctive movies, and there is a strong demand for it."
Issam Rabie -- cellphones and electronics
Issam Rabie, aged 29, sells what he considers to be the most vital products in Mosul -- cellphones and SIM cards.
"Some people work for months just to purchase a smart phone and enjoy its features," he says. "And yet selling smart phones was completely banned during ISIS's rule."
The group cracked down on smartphones, Rabie says, because they didn't want citizens filming and photographing what was happening in Mosul.
If someone was caught with a smartphone, its owner and the device would get taken away, he says.
Consequently, many people downgraded to a regular cellphone that could only make calls and send text messages. But even then, he says you could still get fined for using a phone in public.
After ISIS' departure, demand for smartphones has soared, and Rabie says his shop in the Al-Samah neighborhood is booming.
Abu Ali -- cigarettes and shisha
Smoking shisha or cigarettes was forbidden in public or private under ISIS.
Abu Ali, aged 57, says when the group entered Mosul, he had one month to get rid of his stock. But his shop wasn't the only way to make a profit, as the desire to smoke was high in Mosul.
"The beauty of the situation was that many ISIS members were smokers," he says. "So when cigarettes became scarce after the ban, they contacted undercover distributors."
Now, the public selling of cigarettes is lawful again and Abu Ali says his shop, located in the Nabi Yunus market, sells the most luxurious brands.
Hassan Ali -- toys
Under ISIS rule, the sale of any toys that resembled humans or animals was banned -- a toy that mirrored a figure was seen as a material personification of the image of God.
Hassan Ali, aged 27, owned a toy store in the Al-Muthanna district. He tells CNN that in addition to figured toys, he was also prohibited from selling musical toys.
"During this period, I suffered heavy losses," Ali says. "Many of us were forced to shut down our shops or sell other unprofitable products."
A few months after ISIS's departure, Ali says demand for children's toys is high as a result of the repression children suffered during the occupation, and the limitations they had on possessing toys other than swords or cars.
Abu Ahmad -- barber
Barber shops for women were completely banned under ISIS law. Barber shops for men, however, could operate -- but only within specific rules.
"We were not allowed to design different or weird-looking hairstyles," Abu Ahmad says. "The most important one that we had to stay away from was the faux hawk."
Furthermore, Abu Ahmad and other barbers were prohibited from cutting beards, allowing customers to grow mustaches, threading facial hair, dying hair and using face cleansers.
Abu Ahmad's store shut down at the beginning of the occupation, but is now back in business in the Al-Khadraa neighborhood.
"The profits from this little shop is what I used to provide for my children," he says. "After I shut it down, I found a way to escape Mosul and I have only returned a month ago.
"For more than two years, Mosul lost all its natural features with the presence of ISIS. We only saw darkness during the night and during the day."
Now that the city is liberated, Abu Ahmad says life is finally back to normal.