Developing new materials and technologies is vital for economic growth, developing more efficient and sustainable solutions for generating renewable energies, and advancing the frontiers of human understanding. 2D materials, such as graphene, could be the new disruptive technology, replacing some of the currently used materials. Graphene plays a crucial role in developing groundbreaking electronics, photonics, and optoelectronic applications due to its atomically thin nature and unique physical properties. It is a purely hexagonal, two-dimensional (2D) form of sp -hybridized carbon atoms and the first 2D elemental crystal with remarkable electronic and optical properties, excellent stability and many other qualities. Since the initial discovery of graphene, numerous carbon allotropes, such as phagraphene and the biphenylene network (BPN), have been predicted and many have been synthesized. Following the successful on-surface synthesis of BPN in 2021, the exploration of various exotic carbon allotropes continued, and the search for structural analogues composed of different elements, such as B and N or Ge and S, began. Like graphene, BPN shows many remarkable electronic properties, such as topological states, a recently theoretically proposed multiradical character, anisotropic electronic and thermal transport, as well as potential indications for superconductivity. Consequently, several studies discuss the modification and tunability of the electronic structure as well as mechanical properties by doping and using metal atoms but also boron and nitrogen. Furthermore, investigations into the effect of hydrogenation and halogenation have revealed their impact on lattice strain and electronic structure, resulting in a tuneable band gap depending on the coverage up to the formation of wide band gap materials. Theoretical studies have explored diverse applications for BPN, ranging from the use in electrocatalysis, catalysis, as anode materials, and for hydrogen storage. Undeniably, BPN shows excellent promise as a 2D material with desirable qualities, particularly when doped or functionalized. Due to their high stability, the covalent functionalization of 2D materials is still relatively uncommon and limited to very reactive adsorbates such as radicals or unstable molecules such as benzyne. The functionalization of BPN with covalently bonded, stable, organic molecules could provide new avenues for designing functional materials.