The virial theorem, introduced by Clausius in statistical mechanics, and later applied in both classical mechanics and quantum mechanics, is studied by making use of symplectic formalism as an approach in the case of both the Hamiltonian and Lagrangian systems. The possibility of establishing virial's like theorems from oneparameter groups of non-strictly canonical transformations is analysed; and the case of systems with a position dependent mass is also discussed. Using the modern symplectic approach to quantum mechanics we arrive at the quantum virial theorem in full analogy with the classical case.The virial theorem was originally introduced in classical statistical mechanics (that was the original matter studied by Clausius) but later became important in many other different branches of physics. The quantum mechanical version of the theorem is due to Born, Heisenberg, and Jordan [3] and presently it is a tool frequently used in many body quantum mechanics (e.g. systems of fermions) and in molecular physics; in addition, this matter has also been related to certain fundamental questions arising in nonrelativistic quantum mechanics as the Hellmann-Feynman theorem (see [4]-[18] and references therein). We also mention the importance of the virial theorem in solar and stellar astrophysics [19]. The important point therefore is the wide range of applicability of the virial theorem with applications ranging from dynamical (even relativistic) and thermodynamical systems, to the dust and gas of interstellar space, as well as cosmological considerations of the universe as a whole and in other discussions concerning the stability of clusters, galaxies and clusters of