We introduce the semi-Riemannian geometry. We give some results about Riemannian and Lorentzian manifolds. We explained the Lorentzian causality. We focus on the causality of space-times. We de ne the Lorentzian distance. We compare Lorentzian geometry with Riemannian geometry. We review the Lorentzian warped products and their causality. We focus on the completeness of Lorentzian manifolds and Lorentzian warped products. Then we focus on geodesic connectedness. We give some information about the geodesic connectedness of multiwarped space-times. Lastly, we analyse the relationship between connectedness and completeness of twice warped products under a given condition.