They have a full itinerary, including a charity polo match, a black-tie dinner and a visit to an inner-city charity.
"L.A. is not quite going to know what hit it when the Duke and Duchess of Cambridge arrive," said ABC News Royal Watcher Katie Nicholl.
Prince William will arrive nearly three decades after his grandmother's visit. It was a meeting that Shirley Wilson of the British Home says she'll never forget.
"I belong to daughters of the British Empire. They help raise money to help support this home," she said.
The British Home in Sierra Madre has been home for many ex-pats for nearly 80 years. They served tea to the queen and sent a blanket for William when he was born - a gift quickly acknowledged the day after it was received.
They are devoted royal watchers and believe the Duke and Duchess of Cambridge represent a sea change from past royals
"These two young people have been in touch far more with normal life than their predecessors," said Doris Banks of the British Home.
When the royal couple land in the afternoon at LAX, they'll be greeted by California Gov. Jerry Brown. They will attend a reception in the evening at the British consul-general's home in Hancock Park, where residents are working with authorities to try to keep paparazzi away.
"It should be a little crazy, but fun to have royalty in the neighborhood," said Hancock Park resident Jay Ackerman.
On Saturday, Prince William will play in a charity polo match in Santa Barbara. The cheap seats are $400, while VIP tickets are $4,000. The Duchess will be presenting the trophy to the winning team.
At the Belasco Theatre in downtown L.A., preparations are under way for perhaps the most glamorous show of all. The British Academy of Film and Television Arts, BAFTA, will showcase Brits to Watch, their 42 rising stars, on Saturday night.
The A-list stars of Hollywood are lining up for tickets, reportedly including Jennifer Lopez, Nicole Kidman and Tom Hanks.
It will be a different kind of show Sunday morning when the royals head to Inner-City Arts near Skid Row. The organization focuses on bridging the gap from the art studio to the classroom.
"This really lets the world know that good things, good people, good ideas can come from right here in the homeless capital of America," said Cynthia Harnisch, CEO of Inner-City Arts.