Mong Kok (also spelt Mongkok), less often known as Argyle (see Name section), is an area in the Yau Tsim Mong District on Kowloon Peninsula, Hong Kong. Before the 1994 merger, Mong Kok was part of the Mong Kok District.

The district is characterized by a mixture of old and new multi-story buildings, with shops and restaurants at street level and commercial or residential units above. Major industries in Mong Kok are retail, restaurants (including fast food) and entertainment.

Mong Kok's population density is extremely high. According to Guinness World Records, Mong Kok has the highest population density in the world (mean 130,000 per km or 340,000 per mi) and with a development multiple of four.

Displays at the Chinese University of Hong Kong show some antique potteries, indicating that there might be settlements that early as Jin Dynasty (265-420).

The area of Mong Kok has changed significantly over the years. The heart of the present-day Mong Kok was Ho Man Tin whilst the proper Mong Kok was north of it, near present-day Mong Kok East Station of MTR. With cultivated lands, it was bounded south by Argyle Street, west by Coronation Road (present-day Nathan Road), and east by the hills. To its south is Ho Man Tin and west Tai Kok Tsui. Stream from the hills east offered water for cultivation.

On 10 August 2008 the Cornwall Court fire broke out. More than 200 firefighters were involved in the rescue operation. Four people died, including two fire fighters.

Mong Kok got a lot of negative media attention when it was hit by a number of acid attacks on Sai Yeung Choi Street from December 2008 through January 2010.