This study presents cryo-electron microscopy structures of full-length human ACE2 in complex with the neutral amino acid transporter B⁰AT1, and with the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. The structures were determined at an overall resolution of 2.9 Å, with a local resolution of 3.5 Å at the ACE2-RBD interface. The ACE2-B⁰AT1 complex forms a dimer of heterodimers, with the collectrin-like domain of ACE2 mediating homodimerization. The RBD is recognized by the extracellular peptidase domain of ACE2 mainly through polar residues. These findings provide important insights into the molecular basis for coronavirus recognition and infection. SARS-CoV-2 is a positive-strand RNA virus that causes severe respiratory syndrome in humans. The outbreak of COVID-19 has caused a severe epidemic, claiming over 2000 lives worldwide. The genome of SARS-CoV-2 shares about 80% identity with that of SARS-CoV and is about 96% identical to the bat coronavirus BatCoV RaTG13. The S protein of SARS-CoV-2 may also exploit ACE2 for host infection. The structure of the S protein of SARS-CoV-2 shows that the ectodomain of the SARS-CoV-2 S protein binds to the PD of ACE2 with a dissociation constant of ~15 nM. ACE2 is a type I membrane protein expressed in lungs, heart, kidneys, and intestine. Its primary physiological role is in the maturation of angiotensin (Ang), a peptide hormone that controls vasoconstriction and blood pressure. The PD of ACE2 cleaves Ang I to produce Ang-(1-9), which is then processed by other enzymes to become Ang-(1-7). ACE2 can also directly process Ang II to give Ang-(1-7). Structures of the ACE2-PD alone and in complex with the RBD or the S protein of SARS-CoV have revealed the molecular details of the interaction between the RBD of the S protein and PD of ACE2. Structural information on ACE2 is limited to the PD domain. The single transmembrane (TM) helix of ACE2 makes it challenging to determine the structure of the full-length protein. ACE2 also functions as the chaperone for membrane trafficking of the amino acid transporter B⁰AT1, which mediates uptake of neutral amino acids into intestinal cells in a sodium-dependent manner. Mutations in B⁰AT1 may cause Hartnup disorder, an inherited disease with symptoms such as pellagra, cerebellar ataxia, and psychosis. The structures of the ACE2-B⁰AT1 complex and the RBD-ACE2-B⁰AT1 complex were determined. The ACEThis study presents cryo-electron microscopy structures of full-length human ACE2 in complex with the neutral amino acid transporter B⁰AT1, and with the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. The structures were determined at an overall resolution of 2.9 Å, with a local resolution of 3.5 Å at the ACE2-RBD interface. The ACE2-B⁰AT1 complex forms a dimer of heterodimers, with the collectrin-like domain of ACE2 mediating homodimerization. The RBD is recognized by the extracellular peptidase domain of ACE2 mainly through polar residues. These findings provide important insights into the molecular basis for coronavirus recognition and infection. SARS-CoV-2 is a positive-strand RNA virus that causes severe respiratory syndrome in humans. The outbreak of COVID-19 has caused a severe epidemic, claiming over 2000 lives worldwide. The genome of SARS-CoV-2 shares about 80% identity with that of SARS-CoV and is about 96% identical to the bat coronavirus BatCoV RaTG13. The S protein of SARS-CoV-2 may also exploit ACE2 for host infection. The structure of the S protein of SARS-CoV-2 shows that the ectodomain of the SARS-CoV-2 S protein binds to the PD of ACE2 with a dissociation constant of ~15 nM. ACE2 is a type I membrane protein expressed in lungs, heart, kidneys, and intestine. Its primary physiological role is in the maturation of angiotensin (Ang), a peptide hormone that controls vasoconstriction and blood pressure. The PD of ACE2 cleaves Ang I to produce Ang-(1-9), which is then processed by other enzymes to become Ang-(1-7). ACE2 can also directly process Ang II to give Ang-(1-7). Structures of the ACE2-PD alone and in complex with the RBD or the S protein of SARS-CoV have revealed the molecular details of the interaction between the RBD of the S protein and PD of ACE2. Structural information on ACE2 is limited to the PD domain. The single transmembrane (TM) helix of ACE2 makes it challenging to determine the structure of the full-length protein. ACE2 also functions as the chaperone for membrane trafficking of the amino acid transporter B⁰AT1, which mediates uptake of neutral amino acids into intestinal cells in a sodium-dependent manner. Mutations in B⁰AT1 may cause Hartnup disorder, an inherited disease with symptoms such as pellagra, cerebellar ataxia, and psychosis. The structures of the ACE2-B⁰AT1 complex and the RBD-ACE2-B⁰AT1 complex were determined. The ACE