This article will consider the formative effect of boundaries between activities in directing and deflecting the attention of actors who are seeking to develop innovatory practice at these boundaries. Specific attention will be directed to practices of communication at these boundaries and also to the way in which these boundaries shape the practices of communication themselves. The concept of boundary strength will be developed and discussed. Its utility will be illustrated through reference to an investigation of the consequences of 3 very different examples of attempts at boundary crossing as Local Authorities in England attempt to develop integrated Children's Services from traditional collections of single service agencies (e.g., Education, Health, Social Services). The data will be drawn from a 4 year study of professional learning in and for interagency working directed by the authors and funded within the UK Economic and Social Research Council's Teaching and Learning Research Programme. (Contains 2 tables and 5 figures.)