How to make crispy French fries?
Not to take anything away from the answers already existing for this question, but I want to add one more reference:  Kenji Alt's in depth opus on creating the McDonald's style fry at home.

In summary, his method is to:


Blanche the cut potatoes in water lightly acidified with vinegar, to allow them to cook through while the acid keeps the pectin from decomposing and causing the fries to fall apart.
Par-fry the potatoes (first fry).
Optionally (but preferably) freeze the fries at this point, which actually helps develop the crispiness.  Of course this also lets you do almost all of the work in advance.
Finish-fry and serve.


You will note this is a variant on the traditional double-fry method outlined in Kevin Dickerson's answer.

See the linked article for all of the science, the details, and a linked recipe.