Chloroplast biogenesis and function rely on the import of thousands of nucleus-encoded preproteins from the cytosol. Preprotein import is supported by the Toc and Tic (Translocon at the outer and inner envelope membranes of chloroplasts) complexes, which work cooperatively to translocate preproteins across the double-membrane envelope to the chloroplast interior. Toc159 is one of the preprotein receptors of the Toc complex, is also encoded in the nucleus and post-translationally targeted to the chloroplast, and is comprised of 3 distinct domains: 1) the intrinsically disordered N-terminal Acidic (A-) domain; 2) the central GTPase (G-) domain; and 3) the C-terminal Membrane (M-) domain that anchors the protein to the chloroplast outer membrane (COM) through an unknown mechanism. The M-domain has no known homologues and does not contain a predicted trans-membrane domain, but does contain intrinsic chloroplast targeting information at the extreme C-terminus. The M-domain also contains a predicted β-helix motif, which may be important for anchoring the protein to the COM. We are interested in characterizing the structure of the M-domain and determining the nature of its association with the COM, as part of our larger goal of understanding the role Toc159 plays in protein import into chloroplasts. We are also interested in defining the precise nature of the targeting information contained within the extreme C-terminus of Toc159, elucidating the targeting pathway that is used, and whether other COM proteins use this pathway. We will present our most recent data on the structure, function and targeting of the Toc159 M-domain.