Elemental boron has attracted researchers because of its large number of allotropes, thus providing a variety of scientific aspects within physics and chemistry. Boron compounds and boron nanomaterials have also shown various polymorphs that have been investigated as functional materials for our society. The uniqueness of the boron atom is due to its high frequency of electron multi-center bonding with neighboring atoms, which is still a significant topic in theoretical and computational research. Recently, there have been reports on the realization of two-dimensional (2D) or planar boron nanomaterials, the so-called borophenes. As expected, observations of the various 2D polymorphisms have triggered a considerable number of research lines worldwide. This reprint presents a collection of such papers at the forefront. The contributed papers are transferred from the Special Issue of "New Science of Boron Allotropes, Compounds, and Nanomaterials" in the journal . The issue was launched in 2021, and it aimed to provide a forum for the dissemination of the latest information on boron allotropes, compounds, and nanomaterials.