Ok, let's assume they do exist. The cultural and philosophical differences will probably be too different for us to understand them and even understand they are intelligent. And I don't speak about the probability that either Us or Them can ever meet, or even exchange information.
Leinster's "First Contact" was a very nice story for mid-40s, but it's hard to imagine species from different planets to understand each other.
The best study of a "contact" problem in a popular sci-fi book was made by Stanislaw Lem in "Fiasco", his last big fiction work. It's the book that sums up all his major novels like Magellanic Cloud, Eden, Solaris and Invincible. Agreat novel and unfortunately not as popular as his other books.