Festivities are planned worldwide, culminating with a synchronized smoke at 4:20 p.m.
How the marijuana-loving world came to mark the occasion is believed traceable to five Northern California men now in their 60s with bad backs and graying hair. They are the unofficial grandmasters by virtue of the code they created nearly 50 years ago as students at a suburban San Francisco high school in 1971.
In this Friday, April 13, 2018, photo, the Waldos, from left, Mark Gravitch, Larry Schwartz, Dave Reddix, Jeffrey Noel and Steve Capper sit on a wall they used to frequent at San Rafael High School in San Rafael, Calif. Friday is April 20, or 4/20. That's the numerical code for marijuana's high holiday, a celebration and homage to pot's enduring and universal slang for smoking. And the five Northern California high school stoner buddies widely credited with creating the shorthand slang for getting high nearly 50 years ago now serve as the day's unofficial grand masters.
"We thought it was a joke then," said David Reddix, a filmmaker and retired CNN cameraman. "We still do."