Change Levels are defined in the Service Transition volume of the new ITIL version 3. Changes can take place at three different levels in an organization.
The three levels where changes can be directed are at the Strategic, Tactical and Operational. The easiest translation for these levels is business, service and operations respectively.
Business or Strategic changes relate to the 'direction' that a business is taking. A change at this level would be drawn up and carried out by senior managers. It is likely that new strategic directions or changes to existing strategic thinking would also impact on the provision of services.
service or Tactical changes refer to modifications to existing or new services that are required as a result of changing strategic direction. It is perhaps not appropriate that all service changes are connected to a strategic change, but the connection is a logical one to make.
Operational changes are driven by technology or service changes. For example, if a service change requires higher throughput then that is likely to flow down to an operational level (faster machines, etc.) However, there may also be changes that are forced on the organization (e.g. security upgrades, operating system upgrades, etc.)