International Symposium on Uncertainty Quantification and Stochastic Modeling(Uncertainties 2012), which has taken place at Maresias, city of S˜ao Sebastiao, state of S ˜ao Paulo, Brazil, fromFebruary 26 to March 2, 2012.The meeting was organized on behalf of the Brazilian Society of Mechanical Sciences and Engineering’s (ABCM)Committee on Uncertainty Quantification and Stochastic Modeling, with the objective of providing a proper forumfor discussion of academic, scientific and technical aspects of uncertainty quantification in mechanical systems. Fi-nancial support was provided by the Brazilian Funding Agencies CAPES, FAPESP and CNPq, which are gratefullyacknowledged. Additional operational support from the Structural Engineering Department of S˜ao Carlos Schoolof Engineering (EESC) and from the Brazilian Societies of Applied and Computational Mathematics (SBMAC) andComputational Methods in Engineering (ABMEC) was essential for the meeting’s success.The symposium consisted of 59 oral presentations and 9 keynote lectures covering practical and theoretical aspectsof uncertainty quantification and stochastic modeling, with applications to structural dynamics, nonlinear dynamics,corrosion and damage, structural reliability, optimization, acoustics and vibroacoustics. Based on their contributionsand editorial guidelines, selected presenters were invited to prepare full papers for publication in this special issue.All manuscripts underwent scientific and technical peer review according to the journal standards.The contributions in this special issue include studies on model reduction for dynamics of complex structuresusing a probabilistic approach (Batou and Soize, 2013), reliability-based design optimization of reinforced concretestructures (Aoues et al., 2013), multi-stage bayesian framework for prediction of porous media flow (Ginting et al.,2013), effect of uncertainties on the performance of discrete spatial modal filters (Trindade et al., 2013) and design-point excitation for crack propagation under random loading (Moustapha et al., 2013).In conclusion, we thank the authors for their valuable contributions and also the reviewers for their commentswhich undoubtedly improved the formal and technical value of the articles presented in this special issue.