This study reports the first experimental observation of highly anisotropic and robust excitons in monolayer black phosphorus. Using polarization-resolved photoluminescence measurements, the researchers demonstrate that the emitted light from monolayer black phosphorus is linearly polarized along the light-effective mass direction and centered around 1.3 eV, indicating the presence of highly anisotropic bright excitons. Photoluminescence excitation spectroscopy suggests a quasiparticle bandgap of 2.2 eV, leading to an estimated exciton binding energy of around 0.9 eV, consistent with theoretical results. The highly anisotropic nature of these excitons is attributed to the anisotropic band dispersion of monolayer black phosphorus, which results in strong in-plane anisotropy and enhanced Coulomb interactions between carriers. The study also reveals that the optical and quasi-particle bandgaps of monolayer black phosphorus are 1.31 ± 0.02 eV and 2.2 ± 0.1 eV, respectively, which agree well with first-principles calculations. The findings suggest that monolayer black phosphorus has a large thickness-dependent bandgap tuning range from 0.3 to around 2 eV. The experimental observation of highly anisotropic, bright excitons with large binding energy opens new avenues for exploring many-electron effects in this 2D material and suggests potential applications in optoelectronic devices such as on-chip infrared light sources. The study also provides direct experimental evidence of the highly anisotropic carrier mobility in monolayer black phosphorus, which may be utilized to construct advanced electronic devices and circuits. The results highlight the unique properties of monolayer black phosphorus and its potential for future applications in optoelectronics and electronics.This study reports the first experimental observation of highly anisotropic and robust excitons in monolayer black phosphorus. Using polarization-resolved photoluminescence measurements, the researchers demonstrate that the emitted light from monolayer black phosphorus is linearly polarized along the light-effective mass direction and centered around 1.3 eV, indicating the presence of highly anisotropic bright excitons. Photoluminescence excitation spectroscopy suggests a quasiparticle bandgap of 2.2 eV, leading to an estimated exciton binding energy of around 0.9 eV, consistent with theoretical results. The highly anisotropic nature of these excitons is attributed to the anisotropic band dispersion of monolayer black phosphorus, which results in strong in-plane anisotropy and enhanced Coulomb interactions between carriers. The study also reveals that the optical and quasi-particle bandgaps of monolayer black phosphorus are 1.31 ± 0.02 eV and 2.2 ± 0.1 eV, respectively, which agree well with first-principles calculations. The findings suggest that monolayer black phosphorus has a large thickness-dependent bandgap tuning range from 0.3 to around 2 eV. The experimental observation of highly anisotropic, bright excitons with large binding energy opens new avenues for exploring many-electron effects in this 2D material and suggests potential applications in optoelectronic devices such as on-chip infrared light sources. The study also provides direct experimental evidence of the highly anisotropic carrier mobility in monolayer black phosphorus, which may be utilized to construct advanced electronic devices and circuits. The results highlight the unique properties of monolayer black phosphorus and its potential for future applications in optoelectronics and electronics.