Boyarsky has already answered the question in the comments section.  These are a couple of expositions which put John Tate's contribution in perspective.

 1. Stephen Kudla's chapter on [Tate's
    thesis][1]
 2. Stephen Gelbart's article on [Elementary
    introduction to Langlands'
    program][2].  See the section beginning page 194

  [1]: http://books.google.com/books?id=x3XR0ljIV6YC&lpg=PP1&ots=e47zkJRPWR&dq=Class%2520field%2520theory%252C%2520the%2520Langlands%2520program%252C%2520and%2520its%2520application%2520to%2520number%2520theory&pg=PA109#v=onepage&q&f=false
  [2]: http://www.ams.org/journals/bull/1984-10-02/S0273-0979-1984-15237-6/home.html