The Tonelli existence theorem in the calculus of variations and its subsequent modifications
were established for integrands $f$ which satisfy convexity and growth conditions. In 1996, the author
obtained a generic existence and uniqueness result (with respect to variations of the integrand of the integral functional)
without the convexity condition for a class of optimal control problems satisfying the Cesari growth condition. In this paper, we
survey this result and its recent extensions, and establish several new results in this direction.