This chapter deals with perhaps the most difficult task of conceptualising 3D form and space. First, I examine the constituent parts of 3D form, and then I unfold what a person registers in sequence when entering a space. Light defines how a space is seen, by reflecting off surfaces and form. Design is about expression of identity and 3D form will play a major role in this. 3D interior form is put into three starter groups: the square, circle and triangle families. The chapter continues with illustrations of how junctions and the meeting of surfaces need close consideration and the intrusive corner concept expanded into possible solutions. The early growth of the ‘integrated’ interior is explained with illustrations, culminating with examples of ‘Freeform’ architecture. I finally question what is Deconstructed interior as well as Disintegrated interior?