To avoid overtargeting consumers or targeting them at the wrong moment, mobile ads need to be relevant. Geographically, consumers have been shown to be more responsive to promotional offers from shops that were located close to them. For the lead time of promotions, insights are similar: The closer in time, the better the response. When considering the interplay of time and space, though, the picture becomes more complex. Recipients need enough time to respond given their distance from the promoted venue, but too much time may reduce response rates. It appears that people do not plan too far in advance for events such as movie watching or with small-screen devices such as smartphones. Another context that can affect people’s response to mobile ads is that of the environment - what is going on around people. In a study of mobile promotions during subway rides, mobile campaigns turned out to be more effective on more crowded trains. Even if this finding cannot be generalized to all forms of crowded environments, it clearly shows that context matters. Understanding its impact can help marketers become better gatekeepers by delivering the right mobile ad to the right person at the right time at the right place in the right context.