People multitask (in economists’ language, “engage in joint production”) in a surprising variety of ways. A neat example appeared in Brussels Airport, with a sign saying “charge your phone and laptop.” But the charging was done by you sitting on a saddle and peddling a machine that generated the power charging your device. This combination of activities illustrates the difficulty in classifying activities: Was it work or was it leisure (exercise), to pick two of the major aggregates that I use in my research? Was it an investment of time or was it consumption? In this and many other ways, changing technology renders rapidly obsolete the categories we have created to classify things and activities.