The main difference between Eclairs and Profiteroles is the shape given to the Choux Pastry: one is thin and long while the other one is small and round. The filling is often also different. An eclair is always filled with a cream (whipped cream, pastry cream,...) while a Profiterole can also be filled with Ice Cream - and that's usually how they are served in France. Also, Eclairs are usually finished with a glaze and Profiteroles with a Chocolate Sauce.