Theory of deformation twinning by Bilby and Crocker [B.A. Bilby. A.G. Crocker, Proc. R. Soc. 288 (1965) 2411 is applied to calculate the twinning elements for all possible low index twinning modes in tetragonal, orthorhombic and. ruonoclinic Nd2Si2O7. The magnitude of shear strain was also calculated for each twinning mode. The criteria of small shear strain and minimum shuffling is applied to predict the operative twinning modes for tetragonal, orthorhombic and monoclinic Nd2Si2O7. These predictions of the theory are compared with the available experimental information for analogue oxides and may act as guideline for future experimental work. (c) 2006 Elsevier B.V. All rights reserved.