ITIL V3 comes compartmentalized as five phases, each phase is a book, 5 books in total.
Service strategy is the first phase of ITIL V3. It deals with the business end of service management – strategizing which service to offer to customers and opting for services depends on the market space, the ROI and the customer demand for the service (such as software installation, e.g. painting estimating software).
Once the board of directors decide to introduce a new service, technical people need to burn the midnight oil to give flesh and bones to mere ideas. This is covered in the service design lifecycle.
Post design, it needs to be launched for customers to start leveraging on the service. Service transition looks into it.
Service operation lifecycle manages the maintenance of a service. For example, for your cell phone service to be operational at all times, there are a number of activities running in the background to ensure that it doesn’t fall apart.
Last, but definitely not the least important. Continual service improvement ensures that the service does not stagnate but improves on a regular basis. Remember the verse from the bible – if you are not growing, you are dying. It applies here and everywhere else as well.