This book investigates the stress concentration factor in countersunk holes in orthotropic plates under uniaxial tension load. Finite element analysis using ANSYS was used to build and mesh the geometry of the plate with a countersunk hole, define the boundary and loading conditions, run the analysis and obtain the stress concentration factor results. The effect of several geometric parameters such as plate thickness, straight-shank radius, countersink angle, countersink depth, and plate size; and different material systems on the stress concentration factor was also investigated. Finally, statistical and factorial analyses were applied on the finite element results to establish the relationships between the stress concentration factor and the various geometric and material parameters and to formulate a general equation for the stress concentration factor in terms of the above mentioned parameters.