For the best pies, choose tender, pink rhubarb.
 
Ingredients

Pastry for 2  9-inch Pie Crusts 
1 1/3 to 1 2/3 cups Sugar
1/3 cup All Purpose Flour
1/2 tsp Grated Orange Peel
4 cups fresh Rhubarb, cut up into 1/2 inch pieces
2 tbsps Butter or Margarine

Heat oven to 425* .  Prepare pastry ( could use pre-made pie crusts ).  Stir together sugar, flour, and orange peel.  Turn half the rhubarb into the pie pans, sprinkle with half the sugar mixture.  Repeat the last steps and then dot with butter.  Cover with the top crust which has slits cut in it, seal and flute.  Sprinkle with sugar.  Cover the edges with a 2-3 inch strip of aluminum foil to prevent excessive browning; remove foil last 15 minutes of baking.  Bake for 40 - 50 minutes or until crust is brown and juice begins to bubble through the slits in crusts. 

Variation:
Strawberry Rhubarb Pie:  Substitute sliced fresh strawberries for half the rhubarb and use the lesser amount of sugar. 

If needed put a foil-lined cookie sheet under the pies to keep the stuff from bubbling over to bottom of oven.  Also I butter my crusts with  all over to give a richer color and to add a little flavor.  As always it is up to you and your preferances to make it work.