Deserts are defined by rainfall; the lack of it. Most of the conventional images we conjure like a mirage are of camels and an oasis, of heat, and stinging sandstorms. But this only applies to some deserts.
The cold deserts are the biggest. What we think of perhaps as poles are very much deserts.
I've gone with the twenty largest since this illustrates how many Australian deserts are on the list.
Antarctic 13,820,430 sq km Antarctica
Arctic 13,726,937 sq km Alaska (United States), Canada, Finland, Greenland (Denmark), Iceland, Russia, Norway and Sweden
Arabian Desert 2,330,000 sq km Saudi Arabia, Jordan, Iraq, Kuwait, Qatar, United Arab Emirates, Oman and Yemen
Gobi Desert 1,300,000 sq km Mongolia and China
Kalahari Desert 900,000 sq km Angola, Botswana, Namibia and South Africa
Patagonian Desert 670,000 sq km Argentina and Chile
Great Victoria Desert 647,000 sq km Australia
Syrian Desert 520,000 sq km Syria, Jordan and Iraq
Great Basin Desert 492,000 sq km United States
Chihuahuan Desert 450,000 sq km Mexico and United States
Great Sandy Desert 400,000 sq km Australia
Karakum Desert 350,000 sq km Turkmenistan
Colorado Plateau 337,000 sq km United States
Sonoran Desert 310,000 sq km Mexico and United States
Kyzyl Kum 300,000 sq km Kazakhstan, Turkmenistan and Uzbekistan
Taklamakan Desert 270,000 sq km China
Thar Desert 200,000 sq km India and Pakistan
Gibson Desert 156,000 sq km Australia
Simpson Desert 145,000 sq km Australia
The different ranking on some sites is reflective of their omitting the cold deserts.
The longest desert is also Antarctica (6000 kilometres long, it also has the longest desert coastline, stretching for 17,968 kms), with the Sahara being the longest hot desert. 1200 to 2000 kms north to south, 5000 kms long east to west.
The shortest desert is the comically captioned Carcross Desert, which may be too humid to be a proper desert but is listed anyway.