The opening day of the Scottish event has been designated Fancy Dress Friday for the last two years, with prizes available for festival goers donning the most outlandish outfits.
This year, the theme is The Mad Hatter's T Party, giving fans of Alice in Wonderland the licence to dress as their favourite characters from the book or simply sport some unusual headgear.
"Everyone is more than welcome to embrace the theme or come up with your own ideas," the T in the Park website explains.
The festival runs from July 9th to 11th and is headlined by Muse, Eminem and Kasabian.
Elsewhere, the Beach Break Live festival in south Wales, which began on Monday (June 14th) and runs until Friday, has announced "musical legends" as this year's fancy dress theme.
That means attendees could find an MC Hammer costume goes down well on the Carmarthenshire site.