Is it possible to measure the distance between two texts ? The purpose with this paper is to explore and to compare the different methods that have been used up to now to measure the distance between two texts. The formulas are various and apply sometimes to frequency, sometimes to presence/absence. The objects measured varies greatly with regard to graphic forms, N_grams, lemmas, frequency distribution, grammatical codes, syntactic or semantic structures. The experience from the studies is, nevertheless, that convergence is present.