While an understanding of the dynamics of segregation has begun to emerge, controlling segregation continues to be a complicated problem. The use of time-modulation-via selective baffle placement-in order to suppress segregation in rotating tumblers is explored. Bidisperse (size or density), cohesionless granular materials in quasi-two-dimensional (2-D) rotating containers are studied by means of simulations and experiments. Results are presented in two main configurations for the placement of the baffles, (1) axial placement, and (2) attached to the periphery of the tumbler. Both experiments and simulations indicate that baffles attached at the periphery are ineffective in reducing segregation, while baffles axially located in the tumbler generate periodic flow inversions and dramatically reduce both density and size segregation. Qualitative and quantitative evidence is presented, in terms of the intensity of segregation. Theoretical and scale-up arguments are provided for the practical implementation of this approach. (C) 2008 American Institute of Chemical Engineers AIChE J, 54: 3124-3132, 2008