Queen Elizabeth II, who has served the English throne for 54 years, is celebrating her 80th birthday in a low-key fashion.

The start of the week of celebrations has been marked by the release of a special set of commemorative stamps. Europe's longest-serving monarch has worked with 10 prime ministers, and her net worth is estimated at a value of $500 million.

Buckingham Palace will serve as host on Wednesday for a luncheon for other people born on April 21, 1926. Thursday, the Queen will visit the Chatham House and the British Broadcasting Corporation to mark the 80 years since both were granted coveted Royal Charters and will assist to the release of a specially-commissioned photograph of the monarch by Lord Anthony Snowdon.

On Friday, the date of the Queen's actual celebration, Elizabeth II will spend the day quietly at Windsor Castle with family and friends, many of her subjects having the opportunity to offer their greetings when she will take a walk down on Windsor's cobbled streets.

As she and her husband, Prince Philip, 84, will receive congratulations from youth groups and local dignitaries, the Band of the Irish Guards will play "Happy Birthday."

Later that evening, Prince Charles, 57, heir-to-the-throne, will host a family dinner in her honor. Said to be in good health, the Queen made official visits to 129 countries and plans to visit Lithuania, Latvia and Estonia this year. Still, rumors say that she is starting to slow down and that Prince Charles will soon take over her duties.