Survey research is changing in a more rapid pace than ever before, and the continuous and exponential growth in technological developments is not likely to slow down. Online surveys are now being completed on a range of different devices: PC, laptops, tablets, mobile phones or hybrids between these devices. Each device varies in screen sizes, modes of operationalization and technological possibilities. We define online surveys that are in practice being completed on different devices as mixed-device surveys. This special issue discusses issues in the design and implementation of mixed-device surveys, with the aim to bring survey research to the next level: in our view all web surveys should from now be thought of as mixed-device surveys. Theory and best practices for mixed-device surveys are still in its infancy. The current state of knowledge about the dynamics of taking surveys on mobile devices is not as advanced as necessary in times of rapid change. While current technology opens great possibilities to collect data via text, apps, and visuals, there is little scientific research published about the actual uses and best practices of these applications to increase data quality. Researchers and survey methodologists in particular need to find ways to keep up with fast changing technologies.