We have synthesized the double-layer Aurivillius phase Bi(2)LnNbTiO(9) where Ln = Nd-Gd, Bi. All compounds adopt the orthorhombic polar space group A2(I)am. The magnetic Ln-ion occupies the cuboctahedral position in the middle of the perovskite double-layer, and thus controls the octahedral tilt of the perovskite block. This tilt modifies the ferroelectric displacement of the (Nb,Ti) towards the octahedral faces. This provides a mechanism to systematically modify the polarization. Mn-substitution on the (Nb.Ti) site for Ln = Bi is homogeneous up to x = 0.2. The magnetic moments of In do not order down to 5 K. (C) 2010 Elsevier Ltd. All rights reserved.