The main character is Jacque Lefavre, a "Tamer" about 100 years in the future. The job of a "Tamer" is to be sent via a new and not well understood technology, the "Levant-Meyer Translation," to distant planets where they explore or set up new bases - mostly explore. Very, very few Tamers retire - the large majority of them die during their work.
Lefavre is part of a team that discovers an alien life form that allows people to hear each other's thoughts when all three (the two people and the alien) are in contact. The creature doesn't appear to be sentient at all - it just has really weird properties. The story follows Lefavre in his work, and the repercussions of this new discovery. The book also contains a number of documents, news items and mostly technical reports that allow Haldeman to unload exposition on his reader. I found these worked really well and enjoyed reading them, but saw a complaint over at GoodReads about "infodumps" and poor construction: it's a matter of personal taste. Overall, I found the book an enjoyable read.