Unravelling the diffraction pattern of a twin consists in assigning each observed intensity to the individuals they come from. The unravel process consists in (1) recognizing the presence of twinning; (2) identifying the twin operations; (3) re-indexing the diffraction pattern of the twin. In case of twin lattice quasi symmetry (TLQS) twinning, the presence of twinning appears in the splitting of the diffractions. For twin lattice symmetry (TLS) twinning, instead, the presence of twinning can be over-looked, but the large fraction of unobserved diffractions and the unusual and complex non-space group absences should draw the investigator's attention to the possible presence of twinning. Some general criteria to identify the presence of twinning are presented and discussed with examples taken from the literature.