Science and Education Publishing American Journal of Mechanical Engineering 1 7 2013 11 13 Theoretical Basis of Modal Analysis 173 179 EN Pavol Lengvarsky Department of Applied Mechanics and Mechatronics, Technical University of Košice, Košice, Slovakia Jozef Bocko AJME2013174 10.12691/ajme-1-7-4 2013 10 09 2013 10 18 2013 11 13 There is given the theoretical background of the modal analysis in this paper. In the first part modal analysis, its theoretical and experimental procedure of vibration analysis is defined. In document one degree of freedom system and its behavior, equations and next modification as system of free vibration, harmonic excitation, structural damping is defined. Also, there is defined important property of the modal model - orthogonal property. In the next step is discussed multi degrees of freedom system, its properties, damping and solution.