Provided herein are ligand dimers, compositions thereof, as well as methods of their use. The ligand dimers provided can comprise at least one ligand to a Her receptor and can be used to force dimerization of specific receptor pairs. The forced dimerization of specific receptor pairs can be used to control (e.g., promote or inhibit) signaling, and, therefore, the ligand dimers provided can also be used in various forms of treatment in which such signaling control is beneficial to a subject. It follows that methods for controlling signaling are provided as are various methods of treatment.