Prior to Birthday Letters, Hughes had only explicitly mentioned Plath once before, in the poem "Heptonstall Cemetery" from his 1979 collection Remains of Elmet.

[2] The cover of Birthday Letters is artwork created by Ted Hughes and Sylvia Plath's daughter Frieda.

The cover is made up of violent reds and vibrant yellows, with just a minuscule amount of blue peaking through against a dark background.

[5] The "Ted Hughes controversy" concerned his possible role in Plath's suicide and subsequent attempts at controlling the finished products of her poetry.

Plath had been studying in England on a government grant, and wanted to meet Hughes after being impressed with some of the poems she'd read in a magazine.

With Plath finding trouble in both working on her poetry and teaching, the couple eventually moved back to London by the end of 1959.

In the poem, Hughes describes the blue flannel suit Plath was wearing on the first day she began teaching at Smith College in 1957.

After her death in 1963, Plath's wish to leave behind a meaningful legacy was fulfilled when her Ariel collection of poetry, and her semi-autobiographical novel The Bell Jar, were hailed as masterpieces of modern feminism, causing her to become a feminist icon in the 1970s.