This paper, by highlighting the experiences and reflections of experts and practitioners, aims to increase knowledge of how social impact assessment is managed and handled at various stages of the planning process in major infrastructure investments in Sweden. Interviews were conducted with nine experts and practitioners working with issues of transport planning and social sustainability. The informants represent the national and regional level and three established consultancies. The results largely confirm earlier research, and the area of social impacts assessment in transport planning in Sweden can be seen as being fragmented. Many fundamental issues in the field remain to be addressed for future development, including issues such as public procurement, the role (and competence) of the client, the role (and competence) of the practitioner, how SIA should be included in the whole planning process taking into account the different stages (including how the SIA should be documented, delivered and monitored), how methods should be managed and included, and how the genuine experts should be included, i.e. those living and working in the affected areas.