This text presents and studies the method of so –called noncommuting variations in Variational Calculus. This method was pioneered by Vito Volterra  who noticed that the conventional  Euler-Lagrange (EL-)  equations  are not applicable in Non-Holonomic Mechanics and  suggested to modify the basic rule used in Variational Calculus. This book  presents a survey of   Variational Calculus with non-commutative variations and shows  that most  basic properties of  conventional  Euler-Lagrange Equations  are, with some modifications,  preserved for  EL-equations with  K-twisted  (defined by K)-variations.    

Most of the book can be understood by readers without strong mathematical preparation (some knowledge of Differential Geometry is necessary).  In order to make the text more accessible the definitions and several necessary results in Geometry are presented separately in Appendices  I and II Furthermore in Appendix III  a  short presentation of the Noether Theorem describing the relation  between the symmetries of  the differential equations with dissipation   and  corresponding s balance laws is presented.