The author argues that the decisions primary teachers make about the curriculum need to be informed by well-developed expertise in the subjects they are planning and teaching. This expertise is necessary when teachers are exercising professional autonomy in areas such as curriculum design, securing breadth and balance, and managing curriculum content. The importance of subject expertise is presented against a backdrop of uncertainty about the primary curriculum, the removal of structures and systems that teachers have become used to and the legacy of years of insufficient training for teachers in the non-core subjects. In conclusion, he suggests that professional development needs to build on, rather than discard, curriculum planning used for many years by identifying the principles on which it is organised so that teachers are able to move their practice forward from a secure base.