This book addresses physicists working in generalrelativity, astrophysics and cosmology. The contributionsare based on reports given at a summer school the goal ofwhich was to review modern research for students. The schoolwas centered on the study of gravitational fieldscorresponding to rotating objects of astrophysical interest,under different viewpoints: theoretical, numerical andobservational. Special emphasis is put on the analysis ofinterior and exterior fields of stationary axisymmetricsystems. Lectures and contributions, collected here in PartI, ranged from basic information useful to newcomers totechnical points pertaining to current research in thisarea. Part II contains lectures and contributions on otheraspects of gravitation theory.