  We study existence and uniqueness of Green functions for the Cheeger
$Q$-Laplacian in metric measure spaces that are Ahlfors $Q$-regular and support
a $Q$-Poincar\'e inequality with $Q>1$. We prove uniqueness of Green functions
both in the case of relatively compact domains, and in the global (unbounded)
case. We also prove existence of global Green functions in unbounded spaces,
complementing the existing results in relatively compact domains proved
recently in [BBL20].
