Disclosed herein are peptoids and related compounds, including peptoid affinity ligands for binding and/or purifying immunoglobulins, immunoglobulin fragments or immunoglobulin fusion proteins thereof. Methods of making peptoid affinity ligands and using the same to bind, purify and/or isolate immunoglobulins and related compounds are also disclosed. Such peptoid affinity ligands comprise a peptoid compound consisting of sequentially coupled peptoid residues forming a peptoid backbone, with one or more functional groups appended to a nitrogen of the peptoid residues of the peptoid backbone configured to provide the desired binding affinity.