1 The Helmholtz Conditions and the Method of Controlled Lagrangians ...1 - Anthony M. Bloch. Demeter Krupka and Dmitry V. Zenkov // 2 The Sonin-Douglas Problem ...31 - Demeter Krupka // 3 Inverse Variational Problem and Symmetry in Action: The Relativistic Third Order Dynamics ...75 - Roman Ya. Matsyuk // 4 Variational Principles for Immersed Submanifolds ...103 - Zbyněk Urban // 5 Source Forms and Their Variational Completions ...171 - Nicoleta Voicu // 6 First-Order Variational Sequences in Field Theory ...215 - Jana Volná and Zbyněk Urban