Project-based work constitutes an increasing part of contemporary working life. For the individual worker, project-based work does not only entail performing specific tasks -it also entails equally important aspects of dealing with uncertainty and ambiguity, to create swift trust with new team members, recurrently enter new project, and leave old projects behind. Project-based work can arguably be described as a form of boundary work. This thesis adopts the conceptual lens of liminality in order to illustrate the challenges experienced by the individual project worker, the practices used to deal with these challenges, and the competence developed by the individual to handle projectbased work. In particular, the studies reported here addresses how mobile project workers -more specifically, technical consultants performing their work in client projects -experience and deal with project-based work.The thesis consists of a compilation of five papers and an extended summary. It draws upon on three qualitative studies based on interviews, diaries, and observations. In addition, the thesis offers a systematic review of literature on liminality at work.The thesis identifies four different "liminality practices" that mobile project workers use to deal with ambiguities in their work situation. Moreover, the thesis develops the concept and framework of "liminality competence" to describe the different levels of competence mobile project workers show in relation to dealing with liminality at work. The thesis also provides insight into how high liminality competence is developed and, furthermore, how formal training programs affect mobile project workers' liminal positions and liminality competence.Keywords: mobile project workers, liminality, project-based work, contingent workers, liminality practices, liminality competence SAMMANFATTNING Dagens arbetsliv består i allt större utsträckning av projektbaserat arbete. Arbete i ett sådant sammanhang handlar inte bara om att utföra sina arbetsuppgifter, utan minst lika mycket om att hantera den osäkerhet som arbetslivet i sig medför, att knyta nya kontakter med nya kollegor och att återkommande träda in i nya grupper, samt att avsluta tidigare grupptillhörigheter. Man skulle kunna säga att detta arbete i hög grad är ett gränslandsarbete. För att fånga de krav som ställs på individen, de praktiker denne använder och den kompetens som individen utvecklar i förhållande till den projektbaserade arbetssituationen används i föreliggande avhandling begreppet liminalitet. I denna avhandling studeras hur mobila projektarbetare, mer specifikt teknikkonsulter som utför arbete i kundprojekt, upplever och hanterar projektbaserat arbete.Avhandlingen består av fem artiklar och en kappa. Den grundar sig i tre kvalitativa studier som bygger på intervjuer, dagboksanteckningar och deltagande observationer. Därutöver presenteras en systematisk genomgång av tidigare litteratur som behandlar arbetsrelaterad liminalitet.Studiernas visar att det finns fyra typer av "liminalitetspraktiker" som m...