A sonnet is a 14-line poem written in iambic pentameter with a set rhyme scheme. The most common types are the English or Shakespearean sonnet, which has three quatrains and a couplet, and the Italian or Petrarchan sonnet, which has an octave followed by a sestet. Sonnets were invented in Italy in the 13th century and introduced to English by Sir Thomas Wyatt in the 16th century. Famous sonnet writers include Shakespeare, Spenser, and Sidney.