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Polymorphism can be distinguished by when the implementation is selected: statically (at compile time) or dynamically (at run time, typically via a [[virtual function]]). This is known respectively as ''[[static dispatch]]'' and ''[[dynamic dispatch]],'' and the corresponding forms of polymorphism are accordingly called ''static polymorphism'' and ''dynamic polymorphism''.
Static polymorphism executes faster, because there is no dynamic dispatch overhead, but requires additional compiler support. Further, static polymorphism allows greater static analysis by compilers (notably for optimization), source code analysis tools, and human readers (programmers). Dynamic polymorphism is more flexible but slower—for example, dynamic polymorphism allows [[Duck typing|duck typing]], and a dynamically linked library may operate on objects without knowing their full type.
Static polymorphism typically occurs in ad hoc polymorphism and parametric polymorphism, whereas dynamic polymorphism is usual for subtype polymorphism. However, it is possible to achieve static polymorphism with subtyping through more sophisticated use of [[template metaprogramming]], namely the [[curiously recurring template pattern]].
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