2D semiconducting materials represent an interesting opportunity for the desired scaling of electronic devices. Black phosphorus (PB) is a promising candidate because of its direct gap in the range of telecommunications wavelengths and a comparatively high room-temperature mobility that compares well with bulk Si. However, despite much transport and optical studies, little is known about its momentum-dependent electronic structure. In this thesis, I study the electronic structure of mechanically exfoliated BP using micro-focus angle-resolved photoemission spectroscopy (ARPES). My measurements unveil anisotropic quantum well states in the valence band. I characterize the full dispersion of the quantum well states in flakes of 2 – 9 monolayers thickness, quantify their effective mass and determine a single set of tight-binding parameters describing the experimental subband dispersion for all thicknesses. My data also reveals signatures of many-body interactions, which I characterize experimentally and study with different theoretical models.