Ruby on Rails Directory Rights Issues

I am trying to install bundler and I am getting the following error.

ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /Library/Ruby/Gems/2.0.0 directory.

I bumped into this site and elsewhere and found a general suggestion to install rbenv, which I used with homebrew. I also added Add rbenv init to my shell using the following command:

$ echo 'eval "$(rbenv init -)"' >> ~/.bash_profile

Then I started a new shell so that the PATH changes took effect and then were checked if rbenv was configured:

$ type rbenv
#=> "rbenv is a function"

All still.

Then I try to install bundler again using gem install bundler, and I still get the error

ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /Library/Ruby/Gems/2.0.0 directory.

I also had trouble setting up Python, and I suspect this is symptomatic with the same reason, but I'm not sure what to do next. Any ideas?

I am running Mac OS X 10.9.1