Component classes generally move the task of generating output to the renderer. All JSF components follow it. Render kit is a set of related renderers. javax.faces.render.RenderKit is the class which shows the render kit. The default render kit having renderers for html but it's up to you to make it for other markup languages. Render kit can execute a skin (a look & feel). Render kit can target a particular device like phone, PC or markup language like HTML, WML, SVG. This is one of the best advantage of JSF because JSF doesn't limit to any device or markup.