This was the definitive anthology of science fiction for many years, and was the highest-ranking anthology on polls of best SF books in 1949, 1952, and 1956, and still ranked third in a 1998 poll.
The contents capture the essence of the "Golden Age" of science fiction that began in roughly 1939 but was heralded two years earlier when John W. Campbell became the editor of Astounding Stories in 1937. Only three of these stories are not from Astounding, and one of those is from Campbell's companion fantasy magazine Unknown.
Note the book also includes two articles, by Willy Ley ("V-2: Rocket Cargo Ship") and A.M. Phillips ("Time-Travel Happens!"), not indexed here.