The present invention relates to a process for the activation of double metal cyanide (DMC) catalysts and to a process for the preparation of polyethercarbonate polyols from one or more H-functional starter compounds, one or more alkylene oxides and carbon dioxide in the presence of a double metal cyanide catalyst, characterized in that (α) (α1) the DMC catalyst and one or more H-functional starter compounds are placed in a reactor, (α2) an inert gas, an inert gas/carbon dioxide mixture or carbon dioxide is passed through the reactor at a temperature of 50 to 200° C. and at the same time a reduced pressure (absolute) of 10 mbar to 800 mbar is established in the reactor by removal of the inert gas or carbon dioxide, (β) under an atmosphere of inert gas/carbon dioxide mixture or under a pure carbon dioxide atmosphere, alkylene oxide is added to the mixture from step (α) at temperatures of 50 to 200° C., and (γ) one or more alkylene oxides and carbon dioxide are metered into the mixture resulting from step (β).