In the past six years, public libraries provide a lot of programs, such as library renovation, substantial collections, and diverse reading promotion in Taiwan. It is important that we need to know the outcomes of those programs and readers' satisfaction. Furthermore, it is necessary to identify the effects of six-year reading promotions and collections development plan of the Ministry of Education. Outcome measurement for libraries is that we evaluate the influences or changes from users participating in services or activities by the goal we had made previously. We evaluate what the changes of intellectual, skill, attitude, and behavior from participants in the library activities. Outcome measurement for libraries service and new projects will prove the value of libraries and it is a new thinking of library management. This article examines the definition and methods of outcome measurement for libraries and explores three cases for implications.