This chapter introduces the notion of corollary work as the condition for, or mainstay of mobile knowledge work (MKW). It reviews the ways in which ‘work’ in general is defined, including the contested meanings of ‘knowledge work’ and ‘mobile knowledge work’. It draws on scholarly discussions of visible and invisible work, feminist analyses of social reproductive labour, and computer supported cooperative work (CSCW) deliberations regarding collaborative and mobile work, to develop our conception of corollary work as all those sociomaterial practices that make MKW possible. The chapter concludes by defining corollary work as those emergent sociomaterial practices of place, time, productivity and identity that are reproduced and transformed in every enactment of MKWlife. It is emergent in how worklife itself becomes and is constantly transformed. We give it the status of work because the practices that give it form are resolutely articulated by study participants in terms of how they potentialise MKW.