Shopping cart abandonment of the online shopping process is a major challenge for firms. It describes the phenomenon that a potential customer starts a check out process for an online order but drops out of the process before completing the purchase. On average, 650 out of 1,000 customers do not convert (Baymard Institute 2017), which highlights the managerial relevance and impact of this phenomenon for online firms. Since shopping cart abandonment directly affects an online firm’s sales and revenue, researchers and practitioners likewise are interested in understanding why people leave a website without completing the shopping process and, more importantly, how to reduce online shopping cart abandonment. However, to date, research on these questions is scarce (e.g., Kukar-Kinney and Close 2010) and firms lack guidance how to deal with online shopping cart abandonment. The goal of this study is to investigate effective countermeasures that firms can use to reduce and prevent the likelihood of abandonment and thereby to increase the likelihood of a conversion. We conducted a field experiment in cooperation with a German accessories online retailer over three weeks (n = 8,467 shopping carts) and tested the effectiveness of a reminder pop-up window with a 10% discount vs. a reminder pop-up window without a discount vs. a control group. All online store visitors within the period were randomly assigned to one of three groups once they have put an item in the shopping cart. The pop-up windows appeared once they were about to click on the exit button. Our results indicate that a reminder pop-up window with a 10% discount significantly increases the conversion rate on the website compared to the control group, leading to an increase in revenue of approximately € 5,000. In contrast, a reminder pop up window a discount does not seem to reduce shopping cart abandonment. Further, we will investigate how this campaign affects the retailer’s overall profitability. In addition, using a laboratory experiment (n = 1,041) we replicated and extended our insights on effective countermeasures for shopping cart abandonment. People seem to be more likely to convert when there is a guest checkout option available. In sum, our research has important implications for researchers and online firms how to deal with online shopping cart abandonment.