This paper introduces a new semi-analytical technique that can be applied to calculate the productivity of vertical, horizontal and multilateral wells. The well location and profile can be arbitrary. The reservoir region containing the well must be homogeneous (isotropic or anisotropic) and it may have constant potential or no-flow outer boundaries. Constant rate, constant bottom hole pressure and a combination of these constraints can be imposed on the wells. It is shown that under certain conditions the well productivity is strongly influenced by the pressure drop in the well and the type of conditions that exist at the reservoir boundaries. For multilateral wells the interaction among laterals can also influence productivity. In many cases, conventional techniques can result in large errors.