The Movie vs The Book

I lost the original listing, so I will construct a new one, starting with the first film.  Note:  This may contain spoilers concerning both the books and the movies.  If you don't want to be spoiled, then you probably don't want to read this page.  ;-)

The Princess Diaries

Places of Residence
The first book takes place entirely in New York City.  Grandmere, as she is referred to by Mia, stays at the Plaza hotel, as does her father, Prince Phillipe.  Mia lives with her mother in a loft, located in Greenwich Village.  The movie takes place in San Francisco.  Mia and her mother live in a refurbished fire house.  Mia's grandmother, Queen Clarisse, stays at the Genovian Consulate. 

School
The school Mia attends in the books is a private school called Albert Einstein High School.  It is located in Manhattan.  In the movie, Mia also attends a private school, but it is called Grove High School and is obviously located in San Francisco.  In the books, Mia's worst class is algebra.  Her algebra teacher is named Frank Gianini.  In the movie, her worst class is debate class (also commonly known as forensics).  Her debate teacher's name is Patrick O'Connell, and he is also her history teacher.  In both the book and the movie, Mia's mother, Helen Thermopolis, meets her teacher by attending a parent-teacher conference.  During this conference, her teacher asks her mother out on a date.

Family
There are some pretty big differences between the movie and the book when it comes to Mia's family.  In the book, Mia's father, Prince Phillipe, is the sovereign prince of Genovia (more on that later).  Grandmere is the dowager princess.  In the book Philippe is an only child.  In the movie, Queen Clarisse is the widow of the late King Rupert.  In the movie, Mia's father, Prince Phillipe, died in an accident.  Mia's parents divorced before the accident.  Her uncle (Phillipe's older brother) Pierre renounced his claim to the throne and joined the church (I think this means he became a monk, or perhaps a priest).  In the book, Phillipe and Helen never got married.  The reason why Mia is eligible for the throne is because Mia's father gets testicular cancer.  The treatments for the cancer render him sterile, therefore unable to sire legitimate offspring. 

Friends and Foes
The names of her friend and boyfriend (Lilly and Michael Moscovitz) were kept the same.  In the book, Josh's last name is Richter.  In the movie, it is changed to Bryant.  Lana's surname is also changed - in the book it is Weinberger, but in the movie it was changed to Thomas.  The director changed it so that Lana could sit behind Mia in class (assuming that the student seating arrangement was by surname).  Jeremiah Hart seems to be the 'movie version' of the book's Boris Pelkowski.  Both Jeremiah and Boris are nerds looked down upon by the popular kids.  Both are also smart.  Jeremiah is more into computers, while Boris is a violin virtuoso.  The characters Tina Hakim Baba, Ling Su and Shameeka were left out of the movie.  In the book, Mia's bodyguard is a thirtysomething Scandinavian named Lars.  In the movie, her bodyguard (and driver) is named Joe (who serves as head of security).

Mia's big discovery
In the movie, Mia is told about her royal status by her grandmother, who travels to San Francisco in search of the heir to the throne of Genovia.  Mia visits the Genovian consulate and they have tea in the garden where the queen tells Mia that she is the only legal heir to the throne in Genovia.  In the book, Mia's father calls her to tell her that he cannot father any more children.  Mia doesn't understand why this is such a big deal until he flies to New York and books into the Plaza.  They have lunch at the Palm Court where Mia's father tells her that he is sterile, and that she must be the heir to the Genovian throne.

Genovia
In the movie, Genovia is actually a small kingdom between France and Spain.  It is a country that has no discernible language other than English (which is highly uncommon in Europe, obviously).  Genovia's head of state is the King, who passed away.  Queen Clarisse is serving as regent until the rightful heir can be found.  In most kingdoms, the head of state's role is ceremonial and symbolic.   In the book, Genovia is a principality (like Monaco or Liechtenstein).  It is ruled by the sovereign prince, which would be Prince Phillipe.  The sovereign prince is the head of state, and probably has powers very similar to the sovereign prince of Monaco, which means he can make and reject laws, and has a big hand in every day decisions.

Mia's Personality
Mia's personality and looks are slightly different.  In the movie, Mia is a tall, busty brunette with shoulder-length hair.  At first, it is very curly and dry, but she gets a makeover and it is straightened out.  In the book, Mia is tall, flat-chested and has dark blonde 'triangular' hair (which means that it is probably very frizzy and just touches the tops of her shoulders).  Mia's grandmother takes her to Chez Paolo for a makeover, and her hair is cut short and dyed a lighter shade of blonde.  In the movie, her vegetarianism is hardly mentioned.  It is referred to in one scene - towards the beginning of the movie, where she visits the consulate for the first time.  The security guards are searching her backpack and she says 'please don't crush my soynuts'. 

Other
In the movie, Lilly's TV show is called 'Shut Up and Listen'.  It is produced by the school, and is aired on the school's network.  It could also be aired on a public access channel, because Queen Clarisse is actually watching it in one scene.  My local community college has it's own public access channel, so that is a possibility.  In the book, Lilly's TV show is called 'Lilly Tells It Like It Is' and is apparently the better production.  Lilly funds and produces the show herself, with her friends serving as cameramen, prop handlers and location scout.  She goes on location to shoot footage, edits it herself and pays the public access station for airtime.