Sandwich Cookies are generally composed of two cookies with a filling in between. The cookies can be either hard and crunchy or soft and chewy, depending on the recipe. The filling can vary widely, including cream cheese frosting, ganache, jam or even ice cream.  Whoopie Pies, on the other hand, have a more specific composition. They consist of two round, cake-like cookies with a filling. The texture of a whoopie pie is closer to cake than to a traditional cookie, and the filling is typically sweeter and lighter than the fillings found in most sandwich cookies. While both are delightful treats involving fillings sandwiched between two pieces of yumminess, sandwich cookies offer more variety in composition, while whoopie pies are a specific type of sandwich treat with a cake-like texture.