A number of inadequacies of existing implementation techniques for extending Java™ with parametric polymorphism are revealed. Homogeneous translations are the most space-efficient but they are not compatible with reflection, some models of persistence, and multiple dispatch. Heterogeneous translations, on the other hand, can potentially produce large amounts of redundant information. Implementation techniques that address these concerns are developed. In languages that support run-time reflection, an adequate implementation of parametric, bounded and F-bounded polymorphism is shown to require (reflective) run-time support. In Java, extensions to the core classes are needed. This is in spite of the fact that parametric polymorphism is intended to be managed statically.