"When it comes to a special occasion in British society, the special occasion is not complete without a hat," Hilary Alexander, fashion director at the Daily Telegraph newspaper, says.
"There has to be a hat, it's part of the social fabric."
So what sort of hat should be worn to the royal wedding?
"For most people, the hat is quite serious and frivolous at the same time," Alexander says. "It completes the outfit and it's a finishing touch."
And for those with hair that's hard to tame, Alexander has the answer: "The bigger the hat, the more hair you can hide. So if you're having a bad hair day, on goes the hat and you can face your public."
The royal bride, Kate Middleton, won't be wearing a hat on her big day, but as for her style:
"I think Kate's style, what we've seen so far, is quite restrained. She does like bright bold color from time to time, such as a great mango orange, lovely greens. ... It's never, never outrageous."
And the same goes for Middleton's choice of headwear.
"Unlike princesses Beatrice and Eugenie, for example, who do go for slightly more whacky hats, more eye-catching," she said. "Kate's hats are quite restrained, subtle, they do the job but they don't sort of cause the photographers to go berserk."
Meanwhile, her future in-law, the Queen, is no stranger to hat-wearing.
"I would think the Queen of England is probably the most famous hat-wearer in the entire world," Alexander says.
"She is rarely seen without a hat and her hats always coordinate with her outfits. And they are always in very strong bright colors, one of the things she wants is to be able to stand out in the crowds so people can see her if they've been queuing for hours, perhaps miles away."
There are also practicalities that must be taken into account. "It's important that the hat has a brim that slightly goes up so it doesn't shadow her face," Alexander says.
The much-awaited royal wedding on April 29 will surely be a triumph of a day for hat lovers.
"It's going to be hat central," Alexander says. "It's going to be hats of all shapes sizes and color, every person is going to be wearing a hat."
A wedding in the spring, a season known for unpredictable weather in England, would suggest that hat-wearers consider the waterproof variety.