Nowadays, mechanical industries operate in a highly competitive environment, therefore the process of developing a component from concept through detailed Computer-Aided Engineering (CAE) and performance validation is optimized for reduced development time and increased product performance. To continuously improve the product design and performance and reduce the costs and time to market, the design and performance engineering is shifted more and more towards virtual modeling and simulation processes from the expensive test-based design evaluations. Secondly, the booming introduction of active and adaptive systems in mechanical structures leads to a ‘mechatronics systems’ revolution, which further improves the product performance at the expense of increased system complexity. It is noted that the potential of structural dynamics test and analysis methods for addressing a structural dynamics design assessment or design optimization depends largely on the confidence that one can have in the results. That is, the results must be accurate, characteristic for the actual problem (and not be the result of testing artifacts) and representative for the actual behavior of the investigated structure. In this context, a key aspect is to be aware of the key sources of uncertainty in the designed product, and the impact thereof on the product performance in terms of structural dynamics, crashworthiness and/or acoustics. This paper reviews the main elements of test data and modal modeling uncertainty and assesses the impact of the uncertainty on some typical modeling problems taken from automotive and aerospace industry.