Some will allow dual citizenship, but place conditions that make it difficult to get more than one. E.g., German citizenship law allows dual citizenship if:

> If a child born to German parents acquires another citizenship at birth (e.g., based on place of birth [birth in jus-soli countries mostly of the Americas], or descent from one parent [one German parent and one foreign parent]).

In theory somebody could have two or three nationalities under that law (two parents and place of birth) but no more.