  Violations of the Okubo-Zweig-Iizuka (OZI) rule in $s\bar s <-> n\bar n = 1/2
(u\bar u + d\bar d)$ mixing and $\phi$ production from nucleon-antinucleon
annihilation are reviewed. Possible explanations are examined. We conclude that
the two-step hadronic loops can explain these OZI violations naturally with
proper consideration of cancellations between loops. No conclusive evidence
exists for glueball states, $s\bar sn\bar n$ four quark states, instanton
effects, and strange quarks in nucleon.
