Robert Silverberg 
Collision Course [EPUB ebook] 

The crew of the XV-ftl was looking forward to shore leave, vacation, and a chance to see their families after a month in space. But once they brought back the news that they had discovered aliens, they were doomed to another, and longer, journey.Accompanying them on the return were several technical experts, who seemed to be more interested in squabbling with each other than meeting the first alien race in the history of humankind. But face to face with the blue humanoid Norglans, everyone began to realise just how important these first meetings could be – for they could make the difference between peaceful coexistence in space and interstellar war!(First published 1958)