A protein complex that is involved in the post-translational delivery of tail-anchored (TA) membrane proteins to the endoplasmic reticulum. TA membrane proteins, also called type II transmembrane proteins, contain a single C-terminal transmembrane region. Some ER membrane insertion complex subunits are conserved between different species such as mammals and budding yeast. [ http://www.ncbi.nlm.nih.gov/pubmed/20676083 http://www.ncbi.nlm.nih.gov/pubmed/20850366 ]