This is the first part of a talk given by Prof Andrew Ranicki for the surgery theory study group in the mathematics department of the university of Edinburgh. It is also the talk that he offered for the Festive Opening Colloquium ot the Floer Centre of Geometry in Bochum on the 7th December, 2011. The slides are avaliable on the "Slide shows" section of Prof Ranicki's Website: http://www.maths.ed.ac.uk/~aar/