Cassandra Clare was born to American parents in Tehran. As a child Clare traveled frequently, spending time in Switzerland, England, and France. Clare returned to Los Angeles for high school (Windward School), and from then on split her time between California and New York, where she worked at various entertainment magazines and tabloids including The Hollywood Reporter.
She is also friends with author Holly Black, and their books occasionally overlap, Clare mentioning characters from Black's novels and vice versa, such as Val and Luis from Black's Valiant.
(All information found on Wikipedia)