The geometry of many structures and building forms such as space frames, dome subdivisions and geodesic patterns are derived from any of the known polyhedra, hence the main title of this book 'Polyhedroids', or polyhedron related forms. A proper understanding of their geometry is crucial, as this determines in many aspects the overall form of buildings, the dimensions of structural parts and the directions under which they meet. In this book the basic geometry of polyhedra is treated and also their application in structures with examples from the own practice of the author, sometimes of relatively great span or height. The book is illustrated with many coloured pictures and a whole chapter is filled with anaglyphs, 3D-pictures for the vision of which special spectacles with red and blue glass is needed.