Languages which have expressive power sufficient to refer to its own expressions give rise to the phenomenon of self-reference, which on the other hand leads to incompleteness of some class of formal systems.
In my talk I would like to present some standard and some lesser known method for obtaining self-reference, and some general conditions which entail incompleteness. The presentation is mostly based on results established by K. Godel, W.V.O. Quine and R. Smullyan.