Additive manufacturing (AM) is a rapidly growing technology that continues to gain in popularity industry and academia. The subsequent improvements in AM processes in recent years has led to the production of low cost, lightweight, and complex polymer composite parts. By integrating thermoplastics and thermosets with reinforcing fibers, their mechanical and thermal properties can be improved. The fibers can be arranged in ordered and non-ordered manner in polymer matrices to stimulate superior mechanical and thermal properties. To achieve this, appropriate consideration must be given to their compatibility with the matrices, distribution, concentration, orientation, and aspect ratio within the matrices for different applications including medical (orthotics, implants), aerospace (turbofans), mold design, and automotive (engine parts).