There has been several articles written about Virtualizers. The aim here is to gather all of the pieces of information related to them and to get deeper into the details. This article won't focus on a particular version of JarperReports. Starting by a little bit of background, what is important to understand is the need and use of the Virtualizer in JasperReports. We will then enumerate the situation where a Virtualizer is needed. Moving then to a more technical approach, we will go through the different virtualizers available and when to use them.