  Non-Hermiticity can destroy Anderson localization and lead to delocalization
even in one dimension. However, the unified understanding of the non-Hermitian
delocalization has yet to be established. Here, we develop a scaling theory of
localization in non-Hermitian systems. We reveal that non-Hermiticity
introduces a new scale and breaks down the one-parameter scaling, which is the
central assumption of the conventional scaling theory of localization. Instead,
we identify the origin of the unconventional non-Hermitian delocalization as
the two-parameter scaling. Furthermore, we establish the threefold universality
of non-Hermitian localization based on reciprocity; reciprocity forbids the
delocalization without internal degrees of freedom, whereas symplectic
reciprocity results in a new type of symmetry-protected delocalization.
