Abstract: A heat exchanger for two fluids, especially an oil cooler for oil and water in an internal combustion engine. The heat exchanger is made up of a dividing wall having a meander-like cross section which is bounded by two side covers to form longitudinal channels and having a headering system comprising cross channels, connecting channels, feed channels, and inlet and outlet openings located at each end of the heat exchanger. The heat exchanger is of modular design so that it can be easily expanded by the connection of several heat exchanger units.