In certain aspects, the disclosure provides soluble single-arm heteromeric polypeptide complexes comprising an extracellular domain of a type I serine/threonine kinase receptor of the TGF-beta family or an extracellular domain of a type II serine/threonine kinase receptor of the TGF-beta family. In some embodiments, the disclosure provides soluble single-arm polypeptide complexes comprising an extracellular domain of a type II receptor selected from: ActRIIA, ActRIIB, TGFBRII, BMPRII, and MISRII. In some embodiments, the disclosure provides soluble single-arm polypeptide complexes comprising an extracellular domain of a type I receptor selected from: ALK1, ALK2, ALK3, ALK4, ALK5, ALK6, and ALK7. Optionally the soluble complex is a heterodimer. In certain aspects, such soluble polypeptide complexes may be used for the treatment or prevention of various TGF-beta associated conditions, including without limitation diseases and disorders associated with, for example, cancer, muscle, bone, fat, red blood cells, metabolism, fibrosis and other tissues that are affected by one or more ligands of the TGF-beta superfamily.