# Runtimes

pperl ships two runtimes that share the Perl-language interpretation
but differ in implementation and capability profile. This chapter
explains when to reach for which, what they share, and where they
diverge. For the concrete list of user-visible differences from
upstream Perl 5, see
[Differences from Upstream](differences-from-upstream).

*[Content to be authored: runtime architecture, when to pick p5 vs
pp, interaction between the two.]*