Place butter in a medium bowl and heat in a microwave for about 45-60 seconds, or until melted. (Alternatively, melt in a saucepan over low heat.)
While butter melts make the graham cracker crumbs. Place half of the crackers on a sheet of waxed paper. Cover with another sheet of waxed paper. Using a rolling pin or other cylindrical object like a wine bottle, roll over the crackers to crash into fine crumbs. Add to melted butter and repeat with remaining half. (Alternatively, place crackers in a blender to create crumbs. In this instance you can melt the butter in a small bowl or glass measuring cup and pour into the blender with the crumbs.)
Add maple syrup and stir to combine well.
Press into baking dish and refrigerate when ready to use if you’re going to bake the filling. If you’re making a no-bake pie, bake the crust at 350°F for 10 minutes then cool before pouring in the pie filling.