This is something of a rarity in SF for me, in that I have seen the 1997 film (reviewed here in January 2008) but not previously read the 1985 book. I thought very highly of the film, though, so had great expectations of the book. I was not disappointed.
Ellie Arroway is a radio astronomer in charge of Project Argus, a vast listening post dedicated to SETI – the search for extraterrestrial intelligence. After a discursive few chapters describing her earlier life and how she came to have this job, the reception of the long-awaited message from outer space takes over the story. It is a communication from a far more advanced civilisation, and this immediately kicks off a fierce international political and religious debate about what it means and how to respond to it. It becomes clear that the message is providing instructions concerning a complex machine of unknown purpose, and it is eventually decided to follow the instructions and build it, not without considerable controversy. The machine takes its five occupants (including Ellie) on an incredible journey, but their return merely causes even more problems. Despite this, the story ends on a note of optimism.
To quote his Wiki entry, Carl Sagan was "an American astronomer, cosmologist, astrophysicist, astrobiologist, author, science populariser, and science communicator in astronomy and other natural sciences". His professional knowledge is always evident, as is his understanding of the often political world of big science. There are lots of explanatory passages and he is always willing to park the action in order to include them, which I didn't mind because they are always relevant and interesting. I do like books which inform as well as entertain. Ellie Arroway is an intriguing heroine who readers come to know well, although the other characters are less well described.
Contact makes an interesting comparison with Bill Napier's 2002 book The Lure (reviewed here in April 2011), which also starts with a message from an alien civilisation, and is also well-informed by the author's day job as an astronomer. There is the same emphasis on the political debates about what response to make, and in fact the aliens don't feature at all – the story is all about the impact on humanity of the message. The Lure is more tightly focused than Contact, a gripping thriller rather than a discursive exploration of the issues, but I think that both of them are excellent books in their different ways and very well worth reading.