You missed a few steps: brew install rbenv brew install ruby-build Copy the line it gives you to your shell's rc file and source it/open a new term: rb

You missed a few steps: brew install rbenv brew install ruby-build Copy the line it gives you to your shell's rc file and source it/open a new term: rbenv install 1.9.3-p125 rbenv global 1.9.3-p125 gem update --system gem install rails gem install bundler # optional, recommended When a new version of Ruby comes out: brew update brew upgrade Then just rbenv install and rbenv global it.