There are many virtualization techniques from different vendors out there at the moment and probably many others will come up soon but in any case they can all easily be grouped in three main solutions:

• Emulation
• Paravirtualization
• Hardware Pass-through
  It's important to understand that all virtualization software does the same thing: virtualize physical machines and the services that they provide. You’ll have to decide what you need from virtualization and then choose the best technology that fits that need. You may also use more than one virtualization solution to solve the various needs within your network.

– Alessandra Scicchitano - 2013-01-16