When Sarah Ferguson married Prince Andrew in 1986, she wore a wreath of flowers on her head as she processed down the aisle of Westminster Abbey. Once she emerged from the registry after signing the marriage certificate, she had changed into a tiara for the recessional. Sarah went to the altar as a young lady and emerged on her husband's arm a married woman. Her statement was simple: According to custom for last two hundred years, the tiara has been the official headpiece of married women, and, ahem, dowagers. So why do Miss America winners get to wear them? Maybe because tiaras, aka diadems have always been worn by nobility and very important people. These jeweled crowns are as ancient as civilization itself. The earliest were found in the Greek/Roman world. Goldsmiths created them to crown the heads of statues of their Gods and priests. The Greeks also awarded them to Olympic champions, and higher-ups wore them to mark celebrated occasions. In Egypt the tiara was a symbol of respect to crown the heads of royal and noble mummies. Fast forward a few centuries and once the Bourbon monarchs returned after 1815, it spun off a real show of elaborate jewelry found in the tiaras of the French court. The British likewise made up some of the most memorable and stunning tiaras of the 19th Century. During this time tiaras became associated with weddings, ushering in the birth of the 'matrimonial tiara'.
source 
sourceThe current Miss America . . . getting crowned with this particular tiara means everything.
Queen Alexandra's Kokoshnik Tiara
The following photos and descriptions come from Mandy's Royalty.org: "Queen Alexandra, the wife of King Edward VII, commissioned Garrard's to create this tiara in the style of a Russian peasant girl's headdress. Her sister Princess Dagmar, who had become Empress Marie of Russia, had a similar tiara which was the inspiration for the Kokoshnik.
It is composed of sixty-one platinum bars and filled with 488 diamonds. It is often worn by HM The Queen today.
Queen Mary's "Girls of Great Britain & Ireland" tiara
This tiara was given to Princess May of Teck as a wedding gift. Lady Eve Greville's committee raised the money from "the girls of Great Britain and Ireland" for the tiara, which garnered more than £5000.
May, a German princess, was engaged to Prince George, son of King Edward VII. She would be known later in life as the formidable Queen Mary, Queen Elizabeth II's mentor in all things royal.
This tiara was made by King George III for his wife, Queen Charlotte.
The Cambridge "Lover's Knot" tiara
It is composed of sixty-one platinum bars and filled with 488 diamonds. It is often worn by HM The Queen today.
Queen Mary's "Girls of Great Britain & Ireland" tiaraThis tiara was given to Princess May of Teck as a wedding gift. Lady Eve Greville's committee raised the money from "the girls of Great Britain and Ireland" for the tiara, which garnered more than £5000.
May, a German princess, was engaged to Prince George, son of King Edward VII. She would be known later in life as the formidable Queen Mary, Queen Elizabeth II's mentor in all things royal.
This tiara was made by King George III for his wife, Queen Charlotte.
The Cambridge "Lover's Knot" tiaraQueen Mary instructed Garrard's to create this tiara in 1914, copying the design of a tiara worn by her grandmother, Princess Augusta of Hesse.
The tiara is named for the Cambridge side of Queen Mary's family, of which Princess Augusta was a part. She was married to the first Duke of Cambridge, a son of King George III. Her tiara was set on a base of pearls to match the hanging drop pearls that were suspended from diamond lover's knots. Queen Mary's design for the tiara did not have a base of pearls, but diamonds instead.
This tiara was frequently worn by Diana, Princess of Wales. It was a gift to her from Queen Elizabeth II. "
The tiara is named for the Cambridge side of Queen Mary's family, of which Princess Augusta was a part. She was married to the first Duke of Cambridge, a son of King George III. Her tiara was set on a base of pearls to match the hanging drop pearls that were suspended from diamond lover's knots. Queen Mary's design for the tiara did not have a base of pearls, but diamonds instead.
This tiara was frequently worn by Diana, Princess of Wales. It was a gift to her from Queen Elizabeth II. "
Russia in the mid to late 19th century had a real Renaissance of jewelry designers. This group of artists brought us some of the most magnificent tiaras and settings imaginable. With the crowning of England's King Edward II in 1902 and King George V in 1911, new tiaras incorporating the royal jewels made history. The Paris Opera, became the epicenter for head chic with many a jeweled and plumed woman, strutting one-of-a-kind tiaras. At the turn of the 20th century, more tiaras were worn than ever before. By the 1920s they were still with us but had evolved as elaborate fashion statements worn on bobbed heads some as bandeaux and aigrettes.
1920s tiara
1920s tiara 
Of course nobody gets a better deal or selection of tiaras than the royals. Shown above is Princess Margaret Rose wearing The Poltimore Tiara. Made by Garrards in 1870 for Lady Poltimore, this tiara made the real headlines when HRH the Princess wore it for her wedding to Anthony Armstrong-Jones in May 1960. Margaret's children let go of this grand and beautiful crown at an auction at Christie's in 2006.
HRH: A beautifully tiaraed Princess Grace of Monaco
My Fair Lady
Here's the Great Audrey. The pageant tiara or more commonly known Holly Golightly pictured below, is the tiara we associate with brides today. She was somehow regal, whether faking it til she made it in Breakfast at Tiffany's, or the European aristocrat in Roman Holiday. Note how Audrey could wear these three very different tiaras in the roles she played.
Roman Holiday
Below are two versions of tiaras by contemporary designers.
True Blind Faith
Amy-Jo Tatum
source
I'd call this Lady above the ultimate tiara wearer . . . . She wears this ring of copper not because she is nobility but noble in all she represents which for me transcends any configuration of jewels and settings . . .
For a further, deeper read on this fascinating subject check out, Tiaras, A History of Splendor by Geoffery C. Munn. He's written two books on tiaras, both with some stunning photos and surprising info . . .
My Fair LadyHere's the Great Audrey. The pageant tiara or more commonly known Holly Golightly pictured below, is the tiara we associate with brides today. She was somehow regal, whether faking it til she made it in Breakfast at Tiffany's, or the European aristocrat in Roman Holiday. Note how Audrey could wear these three very different tiaras in the roles she played.
Roman HolidayBelow are two versions of tiaras by contemporary designers.
True Blind Faith Amy-Jo Tatum
source
I'd call this Lady above the ultimate tiara wearer . . . . She wears this ring of copper not because she is nobility but noble in all she represents which for me transcends any configuration of jewels and settings . . .
For a further, deeper read on this fascinating subject check out, Tiaras, A History of Splendor by Geoffery C. Munn. He's written two books on tiaras, both with some stunning photos and surprising info . . .