NASA's Hubble Space Telescope has been providing astounding images of the universe since April 1990 and has led to remarkable discoveries. NASA's James Webb Space Telescope is the next-generation telescope that will peer even deeper into space and unveil even more mysteries. Both of these extraordinary telescopes are now the topics of two free e-books available from NASA. The e-book "Hubble Space Telescope - Discoveries" takes the reader on a tour of some of Hubble's most significant science successes, combined with some of the telescope's technology and history. In the e-book called the "James Webb Space Telescope - Science Guide," readers learn how the Webb telescope will reveal, in much more detail, mysteries of the universe that Hubble is not able to see.