Overcoming the intestinal epithelium barrier is an important challenge for orally administered drugs, specifically for those that elicit poor water solubility and permeability, and several efforts have been developed to address this challenge. Nanosized drug delivery systems constitute one of these attempts to enhance the penetration and permeation of drugs through the intestinal epithelium; however, there remain limitations to be addressed to lead and elaborate an effective oral drug delivery system. A profound understanding of the mechanism of nanoparticle internalization pathways through gastrointestinal epithelial cells, i.e., endocytosis and paracellular transport, is required to overcome these pitfalls. Furthermore, the physical and chemical properties of nanoparticles, including size, shape, charge, surface composition, and particle deformation and degradation, are relevant factors that influence the internalization process and also in the toxicity profile in the organism. In addition, multiple developed and reported strategies for nanoparticles to target the intestinal epithelial cells, to adhere and penetrate the mucus gel barrier, and to perform a differentiated response according to a specific stimulus (i.e., bioresponsive effect) have been described in the relevant literature. Therefore, this chapter will provide a comprehensive depiction of key nanoparticle aspects to help to formulate a rational and effective design to overcome the intestinal epithelium barrier.