Kubrick's former personal assistant, Anthony Frewin, has written a book called Are We Alone?: The Stanley Kubrick Extraterrestrial-Intelligence Interviews. The title is a little misleading: the interviews in the book were commissioned by Kubrick, though they are not interviews with Kubrick.
Kubrick's original intention, when filming 2001: A Space Odyssey, was to begin it with a prologue in which the world's leading scientists discussed the film's cosmological themes. To this end, he sent Roger Caras around the world with a 35mm movie camera, to interview various scientists. In the end, Kubrick did not use the interviews in the finished film, and they have subsequently been lost. All that survives is a written transcript of each interview, and it is these transcripts that constitute the bulk of Frewin's book.
The interview transcripts have already been published, albeit in an edited form, in Jerome Agel's out-of-print The Making Of Kubrick's 2001, a fact that Frewin only mentions in the briefest possible way in his bibliography. Also, most of Frewin's introduction has previously been published (as 2001: The Prologue That Nearly Was) in the Frankfurt Kubrick exhibition catalogue.