Applications of the Lagrange formalism will be given in this chapter for the motion of rigid bodiesRigid body, which leads to the definition of an inertial tensor. The eigenvectors and eigenvalues of this tensor define the main axes of inertia and main moments of inertia, respectively. From the Lagrange function for the rigid body we will derive Euler’s equation of motion, which will be studied for the case of a symmetric heavy gyroscope.