In the investigation about the Roman Law, it�s essential the study, examination and reflection of the great variety of written text concerning Roman Law that has come down to us, with all the difficulties that it represents. The studious will have to consider a series of elements: testimonies, archaeological rest, ideology of the moment... which in many occasions will be essential to know the real meaning of the ancient texts. It is necesary to initiate the investigations with a cientific and faultfinding attitude, since the authors not always reflected in their writings a truth which must be accepted like inquestionable. In adition, in many occasions, we have received the texts retouched, written up of a form that was not the original one, with gaps, added, cuts or modifications. In spite of the shortage of juridica literatura, and considering its great initial production, we have the sufficient one to have a good view of the classical Roman Law. In this article we have tried to give a general point of view of the problems that appear to the romanist when they handle the Roman Law sources. We will deal the problem of interpolations determining a guideline that allow the discovery in the texts. Finally, we�ll study, as a example, a series of fragments of Publio Juvencio Celso. Metodological criteria will help in the scientific study of Roman Law, but do not forget that the good making and the good sense of the investigator should prevail to obtain accurate conclusions.