One of the challenges in reservoir simulation today is the a gap between the increasing level of detail in geomodels and the capabilities of the comercial reservoir simulators. The most common solution to overcome this gap is the use of upscaling techniques that capture subscale heterogeneities in an average sense. Subscale hetereogeneities can in some cases have great impact on the global flow field that cannot be captured using upscaling techniques. Multiscale modeling of flow in porous media enables direct simulation on detailed geomodels without averaging in an efficient and accurate way. The presentation explains the basic principles behind multiscale modeling of flow in hetereogeneous media.