Crime Prevention through Environmental Design (CPTED) is a method of reducing crime through the design and manipulation of the built environment. Based upon the Opportunity Theories of crime, CPTED focuses upon blocking opportunities for criminal behaviour through subtle techniques to maximise informal surveillance, guardianship and maintenance, to minimise through movement and to set standards of physical security that are proportionate to crime risk. This chapter will discuss the principles of CPTED and the theories from which it evolved. It will explore the effectiveness of these principles, both individually and combined, in reducing crime, before exploring how CPTED is applied in practice