Tired of diagramming your origami models? This book provides an alternative 'language' for communicating how to fold models. It is over 25 years since John Smith first evolved OIL. At that time all diagrams had to be drawn by hand. OIL was designed to be written or typed (this was before the days of PC word processing). The situation now is very different / computers make it much easier to prepare complex diagrams than previously. However the extensive use of E- mail / in which only ASCI symbols can be sent suggests that there may still be a place for OIL. Certainly there has been much interest from those who are looking for new ways of providing folding instructions or analysing folding sequences. He has made a few amendments to the original OIL. The angle of a corner is now shown as X if it is greater. I have adopted the double ended arrow to show a fold which is to made and then opened up again. A new instruction is included to show a ‘tuck in’ command. On occasions it is useful to locate a point or line terms of an existing crease line and the lower case letters have been used for this. OIL is most suitable for relatively simple sequentially flat-folded models. It can handle complex folds since all origami is formed from connected or overlapped polygons. However the definition matrices become rather cumbersome to handle.