When making bisque, the shells are roasted and then simmered to produce a highly flavorful stock which is then thickened. The meat itself is added to the bisque near the end of cooking.
Bisque can be thickened with rice, which is the traditional method. Modern bisques are often thickened with roux. Additionally, although a classic bisque is made only with shellfish, some thick soups made with vegetables, poultry or meat are sometimes referred to as bisques.