The migration of mobile particles through porous networks is restricted when the size of the migrating particles approaches the size of pore throats. In this case, single particle retention or entrapment by bridge formation takes place. Experimental results show that bridge formation and stability are controlled by particle shape, relative throat-to-particle size, and skeletal forces. Forced-vibration studies provide additional insight into bridge stability and the potential for vibration-based unclogging, and show that it is easier to prevent bridge formation than to destabilize already formed bridges. Results from these pore-scale studies are relevant to filter clogging and unclogging, water and oil extraction, sand production in oil wells, and in food grain, aggregate and powder handling operations.