In 2012 I wrote how to install G77 on Ubuntu >=9.04. However that approach no longer works (yet that particular blog posts gets lots of hits because of a link from stackoverflow). So here are some updated instructions which work for Ubuntu >= 14.04.
It is possible that you still need to install g77 to compile a Fortran program on your latest version of Ubuntu, but it isn’t the repositories!! Don’t worry, it is easy.