ABSTRACT: The article examines the general motion of an arbitrarily asymmetric homogeneous rigid body in a fluid medium. Through a defined new theorem – Theorem for change of the generalized momentum of a rigid body, and new Lagrange equations in structure, called Condensed Lagrange equations, the differential equations describing the spatial movement of the body are derived in matrix form. With a new theorem for the flow of an asymmetric solid body from a fluid flow, the existence of a destabilizing aerodynamic moment has been proven. A new full aerodynamic force matrix is defined. The spherical component of body motion is accounted for by gimbal angles. The article is entirely theoretical. It is a foundation upon which other publications on the motion of solids of a particular shape in a fluid medium have been developed.