 <p>I decided to post an answer to try and explain this situation for anyone else that arrives here from Google.</p> <p>As David points out, to fix this error...</p> <pre><code> uninitialized constant Excel::Iconv </code></pre> <p>...you'll have to require "iconv":</p> <pre><code>require "iconv" require "roo" </code></pre> <p>This is because the Roo gem calls <code>Iconv.new</code> in its internal Excel class but Roo forgot to require "iconv" itself, so you're forced to do it. It's a bug. It's no different than calling <code>Set.new</code> without <code>require "set"</code></p> <p><strong>Iconv is part of Ruby 1.8 and 1.9's standard library.</strong> You don't install it. It's already there.</p> <p>However, it's worth pointing out that Iconv is deprecated in Ruby 1.9 and removed in Ruby 2.0.</p>