An extensive investigation of twin structures in lanthanum aluminate single crystals at room temperature has been undertaken using White Beam Synchrotron X-Ray Topography (WBSXRT). Twin configurations, directly observable via orientation contrast, were found to comprise both large-volume, macroscopic twins and thick twin lamellae. Positional shifts of twin domain images with respect to matrix images, arising from the mutual misorientation of diffraction vectors, were measured on x-ray topographic images recorded from the (220)rhom planes approximately parallel to the specimen surface and compared to calculated values in order to solve the twin laws in this system. The dominant twin operations were found to be (101)rhom, (011)rhom, and (112)rhom mirror reflections. The potential influence of the twins on the growth of epitaxial Ba2YCu3O7−δ thin films is discussed.