The work concerns dynamic similarity criteria of various phenomena occurring in aerodynamics of buildings and structures, hydraulics and fluid dynamics derived from ratios of forces and forces moments affecting these phenomena. It consists of three parts. Part I concerns the bases of dynamic similarity criteria formulated in such a way in relations to the problems of fluid–solid interaction at different fluid–solid relative motions. At the end of this part, authorial method and procedure for determination of dynamic similarity criteria in fluid–solid interaction issues have been presented.