This article presents a viable approach to mobile 3-D printing in which a large object is printed in segments. The printer’s motion between printing each segment is localized precisely using the novel procedure of simultaneous localization and additive manufacturing (SLAAM), enabling the joining of subsequent segments while also maintaining overall geometric compliance of the printed part. SLAAM achieves sub-mm accuracy on objects over 400 mm long. SLAAM demonstrates the importance of fusing local (3-D scanner), and global (total-station range finder) sensing, and of maintaining, and updating estimates of the printed part geometry in a global frame. A six-parameter representation for a printed object’s planar surfaces, consisting of the plane’s normal vector, and a 3-D point on the planar patch itself, demonstrates good performance even in the presence of high odometry error.