We all run bundle install so we can use some gem or other, sometimes several times a day. But what does it do, exactly? How does Bundler allow your code to use those gems? Why do we have to use bundle exec? What's the point of checking in the Gemfile.lock? Why can't we just gem install the gems we need? Join us for a walk through the reasons that Bundler exists, and a guide to what actually happens when you use it. Finally, we'll cover some Bundler "pro tips" that can improve your workflow when developing on multiple applications at once.