In this paper the methods of generating reliable durability and service life data are discussed. They may be categorized as follows: 1. long-term aging tests, 2. tests performed in laboratories as combined with long-term aging tests, and 3. theoretical/analytic methods as combined with long-term aging tests and laboratory tests. It is evident that all the above mentioned methods are needed to provide reliable durability and service life data and to develop models for service life design. Usually reliable service life models can be developed only by combining field tests to some laboratory tests and/or theoreti-cal/analytic modeling. Computer simulation might be a powerful tool in service life modeling especially when the variations in environmental conditions, interaction between different deg-radation types and the effects of protective measures such as coatings need to be considered.