This is the third of Blish's books of criticism and was published posthumously - it is also the most varied and the best. In addition to essays on SF themes there are pieces about music and the wider world of letters. There is also a very candid and revealing autobiographical piece and an equally candid and revealing interview conducted by Brian Aldiss. An appendix consists of a very thorough bibliography of Blish's work, including variant titles, foreign language editions and work in all genres. (Blish wrote for sports and detective story magazines when under serious financial pressure.)
I strongly recommend this to all Blish fans - find out how autobiographical some of his books and stories are, what Blish thought of John Cage and what the most realistic dream-novel in English is, amongst many other things!