In recent years, there has been growing research regarding the online nature of visual working memory (VWM). These online aspects are arguably the defining attributes of working memory, but they are challenging to study using traditional behavioral paradigms. One powerful tool to examine online processing in VWM is the contralateral delay activity (CDA), the ERP marker of VWM. We review studies that convincingly demonstrated that the CDA is a unique marker of VWM activity. This specificity joins the excellent temporal resolution of the CDA and the fact that it can be measured not only during memory retention but also when items are visible on the screen, to make the CDA an ideal tool for studying the online processing of items still within view. We present several lines of research that successfully utilized the CDA to uncover the role of VWM in online processing. Finally, we present basic guidelines for using the CDA to study online processes, along with examples from our recent research. We hope that this will enable more researchers to capitalize on the CDA’s advantages, allowing new discoveries to be made regarding VWM as an online workspace.