A 1 second delay on an e-commerce site can result in a 7% reduction in your conversion rate; but profiling isn't just important in e-commerce when limited resources are available. Profiling is really important and there are now a host of tools to help you profile your application through means other than naive profiling. In this talk we'll look at how to identify bottlenecks in your application using a variety of tools; and how we can use those profiler results to improve our Symfony applications' performance.