ITIL stands for Information Technology Infrastructure Library. ITIL was first published in the 1980s, with version 2 released in the mid 1990s and version 3 released in 2007.
ITIL v3 changes the way that IT professionals look at the challenge of managing infrastructure. The concept of the "lifecycle" has been introduced (a concept that has been in place for many years in other frameworks).
The ITIL v3 lifecycle centers on 5 logical volumes. Service Strategy, Service Design, Service Transition, Service Operation and Continual Service Improvement
At the core of ITIL v3 is the key message that the value for an IT service is defined by the customer who is (a) using and (b) paying for that service. The primary difference between ITIL v2 and v3 is that with ITIL v3 the framework is designed to "integrate with the business". In ITIL v2 the framework was designed to "align with the business".