Measurements of adsorption probabilities are the most common ways to gain information about the dynamics of gas-surface interactions.  This knowledge is pertinent for a considerably large number of technical applications, since the adsorption of a gas phase reactant is the first elementary step in all heterogeneously catalyzed surface reactions.  Therefore literally tens of thousands of publications deal with this research topic.  However, during the last few years, a new effect has been observed experimentally and addressed theoretically, namely the enhancement of adsorption by pre-adsorbates.  The presented review will, in contrast to prior reviews about adsorption dynamics, be focused on a discussion of this so-called “adsorbate-assisted adsorption”.