The sestina is not a common form in English poetry, although when done right, it can be one of the most powerful. It is a poem of sixes: six stanzas, each comprising six lines (also known as sestets but known sometimes as ‘sixains’: like ‘quatrains’ but with six instead of four lines), with a final tercet – a concluding ‘envoi’ – bringing the whole poem to a close. So, 39 lines in total, using just six different end-words as the ‘rhymes’. What is a sestina, and what is the sestina used for? How can such a complex and difficult form be used by a poet to express things effectively? Poets as varied as Sir Philip Sidney, Elizabeth Bishop, and Algernon Charles Swinburne have left their mark on this most challenging, and yet rewarding, of poetic forms.