Ultracold molecules provide an ideal platform for exploring the fundamental aspects of quantum physics and chemistry. Diatomic molecules with permanent electric dipole moments have already been employed to achieve the first ultracold, controlled chemical reactions, perform precision measurements, and enable quantum simulations of many-body dynamics. Moreover, the prospects for their application in quantum computing have recently driven the development of single-molecule control using optical tweezers. The rapid progress in this field has motivated an increasing number of research groups worldwide to begin investigating polar molecules at ultralow temperatures. A detailed understanding of the molecular electronic structure is essential for the development of such experiments. This presentation will focus on the emerging challenges in investigating the interactions of molecule–molecule and molecule–atom systems, including CaF + CaF, CaF + Ca, and He + He .