This chapter is devoted to development, planning applications and their determination might seem superfluous given the many contributions to the wider planning literature. It responds to that lacuna by rehearsing some of the key provisions in planning law and procedure that are steering the transitional trajectory of planning practice in Northern Ireland. The chapter considers the following matters: the meaning of development, the planning application, neighbour notification, material planning considerations, prematurity, the contribution of a public local inquiry, planning application decisions, planning appeals and, finally, completion notices. It relates to the weight to be given to different material planning considerations in determining a planning application. The chapter has ranged widely across the development management situation within Northern Ireland and has combined elements of legislation, planning policy and case law to offer a succinct account of how planning applications are framed and how they are determined.