  I discuss the correspondence between realistic four dimensional free
fermionic models and $Z_2\times Z_2$ orbifold compactification. %I illustrate
this correspondence for one particular example. I discuss the properties of the
$Z_2\times Z_2$ orbifold that are reflected in the realistic free fermionic
models. I argue that the properties of the realistic free fermionic models
arise due to the underlying $Z_2\times Z_2$ orbifold compactification with
nontrivial background fields. I suggest that three generation is a natural
outcome of $Z_2\times Z_2$ orbifold compactification with ``standard
embedding'' and at the point in compactification space that corresponds to the
free fermionic formulation. I discuss how quark flavor mixing is related to the
compactification.
