This paper presents the results of an extensive experimental campaign on 16 fat-slab specimens with and without punching shear reinforcement. The tests aimed to investigate the infuence of a set of mechanical and geometrical parameters on the punching shear strength and deformation capacity of fat slabs supported by interior columns. All specimens had the same plan dimensions of 3.0 × 3.0 m (9.84 × 9.84 ft). The investigated parameters were the column size (ranging between 130 and 520 mm [approximately 5 and 20 in.]), the slab thickness (ranging between 250 and 400 mm [approximately 10 and 16 in.]), the shear reinforcement system (studs and stirrups), and the amount of punching shear reinforcement. Systematic measurements (such as the load, the rotations of the slab, the vertical displacements, the change in slab thickness, concrete strains, and strains in the shear reinforcement) allow for an understanding of the behavior of the slab specimens, the activation of the shear reinforcement, and the strains developed in the shear-critical region at failure. Finally, the test results were investigated and compared with reference to design codes (ACI 318-08 and EC2) and the mechanical model of the critical shear crack theory (CSCT), obtaining a number of conclusions on their suitability.