The invention relates to a heat exchanger, for example an indirect air cooler, in which the air, for example compressed charge air of an internal combustion engine, is cooled for example by means of liquid in at least two stages which directly adjoin one another and which are formed in a cooler block which is arranged in a housing, wherein in the cooler block there are arranged flow paths for the liquid, for example, and flow ducts for the charge air, for example, wherein the charge air enters into the housing and flows through the flow ducts of the at least two stages in succession.