The moment a web browser requests a page, Drupal begins running a complex series of steps that result in a fully rendered page being returned to the browser. With every page request, Drupal has to do those same calculations, so understanding them is key to making the best development decisions for your modules or sites.

In this chapter you will learn what happens when a Drupal URL is requested, for instance, this page's URL, 'inside', which maps to the internal path, node/84.