Iambic pentameter is a rhythmic pattern in poetry that consists of ten syllables, with stress on every other syllable. It is a line of verse composed of ten syllables arranged in five metrical feet (iambs), each of which consists of an unstressed syllable followed by a stressed syllable. The term "iamb" refers to a poetic foot of two syllables wherein the first syllable is short or unstressed, and the second syllable is long or stressed. The term "pentameter" means five meters, so a line of poetry written in iambic pentameter has five feet or five sets of stressed and unstressed syllables.

Iambic pentameter was first used in ancient Greek poetry, but it gained popularity in English poetry in the sixteenth century, thanks in large part to Shakespeare. Shakespeare used this meter because the rhythm of five beats per line closely mimicked spoken English at the time. Furthermore, it provided just enough structure to challenge him creatively.

Iambic pentameter has been the predominant meter in English verse since the 16th century. Its unstressed-stressed beat is similar to that of a human heartbeat, and it has been used by notable and influential poets, including John Milton, Percy Bysshe Shelley, Robert Browning, Alfred Lord Tennyson, and Alexander Pope.

Some reasons why writers choose to use iambic pentameter include tradition, rhythm, and emphasis. Although few modern writers structure their works in iambic pentameter, many sprinkle it in now and again for dramatic effect.