The British royal family is like other families, made up of spouses, children, grandchildren, grandparents, uncles, aunts and cousins. The head of the British royal family is Queen Elizabeth II, and she is the one who decides who are bona fide members of the family and what titles they will carry.

To answer your question -- a duke is the highest rank you can achieve without being a king or a prince. Historically a duke is a high-ranking nobleman, land-owner or a prince, and in feudal times was the lord over part of the country. Today the titles are largely symbolic and there are 28 dukedoms. Some people (like Prince Charles) have several dukedoms and some dukedoms are unassigned. When a duke who does not have an heir dies, the title returns to the royal family to be given out to someone new.

Not everyone who carries the title duke or earl is a member of today's royal family. Britain has a system of peerage, which ranks members of the nobility and aristocracy. Many titles of nobility were won many years ago through great wealth, favors to the king or good deeds and are passed on from one generation to the next. This is known as the inherited peerage. For example, Earl Spencer, the brother of the late Diana, Princess of Wales, is the ninth man in his family to carry that title. Before he became Earl Spencer (note that the practice is to drop the "of") upon the death of his father, he was known as Charles Spencer or as Viscount Althorp, a title that his son, Louis, now carries.

Other noble titles are given on merit or on special occasions. The life peerage are titles that the monarch confers on exceptional people during their lifetimes, and those titles do not pass to children or descendents. Margaret Thatcher, the former prime minister of Britain, is now Baroness Thatcher. The British prime minister consults with the queen about who is deserving of a life peerage, and several people are elevated to the peerage every year. Life peers get a seat in the House of Lords, but a law passed in 1999 limits the right of hereditary peers to have a seat.

The order of the titles in British Isles nobility from highest to lowest are:

• Duke (and duchess): The name is derived from the Latin dux, which means leader. Most dukedoms carry a place name, although that means little to the modern titles because the holders are not the sovereigns of a land area.
• Marquess or marquis (and marchioness): This title appeared in England with the Norman conquest and was given to nobles who were in charge of border areas. The name is related to older words for a frontier.
• Earl (and countess): The name comes from a Norse word, jarl, which meant leader. It is equivalent to a count in European nobility.
• Viscount (and viscountess): Pronounced VI-count, this title derives from the Latin comes for a companion and was sort of an assistant nobleman in the old days.
• Baron (and baroness): The lowest rank of nobility came to England with the Normans, also, and the word is derived from the Norman word for a freeman. If you have a life peerage this is the highest title you can carry.

• Baronet: This title is granted to members of the upper classes, referred to as the gentry. The story is that King James I created the title to raise money.
• Knight: In medieval times, knights were the soldiers of the king or of princes. Now, the queen grants knighthood to her subjects who have achieved great success in their professions. Paul McCartney, the former Beatle, has been knighted. The female equivalent is dame.
• Esquire: In medieval times, an esquire was a candidate for knighthood. Nowadays, it is applied to members of the gentry just below knights.

According to the royal family's official Web site, here are the members of the family today:

• Queen Elizabeth II. When Elizabeth Alexandra Mary was born in 1926, no one expected her to become the queen. Her father, the Duke of York, was Prince Albert, the second oldest son of King George V, and his older brother, Prince Edward, was the heir apparent to the throne. Prince Edward did become King Edward VIII when George V died in early 1936. But in one of the most famous scandals of the 20th century, Edward abdicated the throne because he wanted to marry a twice-divorced American woman named Wallis Simpson. So, in late 1936, Prince Albert became King George VI, and his older daughter became the heir presumptive, meaning that unless her parents had a son, she would succeed to the throne. Elizabeth became queen at her father's death in 1952.
• Prince Philip, the Duke of Edinburgh. The queen's husband, like the queen, is a great-great-grandchild of Queen Victoria, and he was a member of both the Greek and Danish royal families. He spent a great deal of his childhood in England and served in the Royal Navy. He gave up his royal title and became a British citizen as a young adult. He received his noble title just before he and then Princess Elizabeth wed in 1947. He can't be king because that would actually give him a rank higher than his wife's.
• Queen Elizabeth, the Queen Mother. Born Elizabeth Angela Marguerite Bowes-Lyon, the widow of King George VI celebrates her 100th birthday Aug. 4, 2000. She is beloved in Britain, not just because of her royal standing, her aristocratic birth and her grandmotherly demeanor, but because she stayed in London during the horrible bombing in World War II when she could have taken her children to a safer place in the countryside. She and her daughter are the only two members of the royal family who are referred to as "Her Majesty," an address that is reserved for kings and queens. Everyone else in good standing is "His Royal Highness" or "Her Royal Highness."
• The Prince of Wales. The queen has given her oldest son, Prince Charles, several titles, chief among them prince of Wales. That is the traditional title carried by the heir to the British throne. He is also Duke of Cornwall, Duke of Rothesay, Earl of Carrick and Baron Renfrew, Lord of the Isles, and Prince and Great Steward of Scotland. His sons, Prince William and Prince Harry, are second and third in the line of succession after Charles. Their mother, of course, was Diana, whose death in 1997 caused an outpouring of grief across Britain and around the world.
• The Duke of York. The queen's second son, Andrew, is also Earl of Inverness and Baron Killyleagh, titles his mother gave him when he married. His wife, Sarah Ferguson, became the Duchess of York, and even though the couple divorced in 1996, she is known as Sarah, Duchess of York. She lost the right to be addressed as "Her Royal Highness" though. Their daughters are Princess Beatrice and Princess Eugenie. Because Prince Andrew has no sons, his title will not be passed on to an heir. It is the crown's property, in a sense, and upon the current Duke of York's death, a king or queen in the future could give the title to another man.
• The Earl of Wessex. The youngest son of the queen prefers to be called Edward Windsor when he is working as a television producer, but he is listed as the Earl of Wessex in the royal family. He became a earl at his marriage in 1999 to Sophie Rhys-Jones, who is now the Countess of Wessex. It is unusual for the son of a sovereign to have a title no higher than earl.
• The Princess Royal. The queen gave her only daughter, Princess Anne, this special title in 1987. It is a title that traditionally can only be given to the monarch's oldest daughter, but not all oldest daughters get the title. The Princess Royal, married for the second time and the mother of two, is considered the hardest working member of the royal family. She sponsors many charitable causes.
• The Princess Margaret, Countess of Snowdon. The queen's younger sister and only sibling became Countess of Snowdon when her then-husband was named Earl of Snowdon at their marriage in 1960. They have been divorced since 1978. Their two children are Lord Linley and Lady Sarah.
• Princess Alice, Duchess of Gloucester. Princess Alice is the widow of the Duke of Gloucester. Her husband, Prince Henry, was the third son of King George V, the queen's grandfather. Her son is now the Duke of Gloucester.
• The Duke and Duchess of Gloucester. Prince Richard is Princess Alice's son and the queen's cousin, and the duchess is his wife, the former Birgitte van Deurs. He inherited his father's title, even though he was a second born son because his older brother died in an accident some years before his father died.
• The Duke and Duchess of Kent. The duke is the queen's cousin, Prince Edward. His father was the fourth son of King George V. The Duke of Kent inherited his title from his father, who died in an accident in 1942. The Duchess of Kent is the former Katharine Worsley.
• Prince and Princess Michael of Kent. Prince Michael is the younger brother of the Duke of Kent. The prince's wife is known as Princess Michael of Kent, even though her given name is Marie-Christine. That is the nobility's way of indicating that she is a princess by marriage, not by birth. Prince Michael is no longer in the line of succession for the throne. He gave up his spot when he married Princess Michael, a Roman Catholic divorcee, but the two still perform royal duties and represent the queen at weddings and funerals.
• Princess Alexandra. She is the sister of the Duke of Kent and Prince Michael of Kent. Her husband is Sir Angus Ogilvy, and they have two children.

• The official Web site of the British royal family
• A set of questions and answers about British royalty
• Insight magazine, a monthly guide to the royal family
• An unofficial British royalty site
• A guide to noble titles