In a February 1966 letter to her artistic confidant, Robert Lowell, Elizabeth Bishop tellingly grouped four midcentury poets: Lowell, Randall Jarrell, John Berryman, and herself. For Bishop--always wary of being pigeonholed and therefore reticent about naming her favorite contemporaries--it was a rare explicit acknowledgment of an informal but enduring artistic circle that has evaded the notice of literary journalists for more than forty years. Despite the private nature of their dialogue, the group's members--Bishop, Lowell, Jarrell, and Berryman--left a compelling record of their mutual...