Approximately 40%-60% of developing drugs failed during the clinical trials because of ADME/Tox deficiencies. Virtual screening should not be restricted to optimize binding affinity and improve selectivity; and the pharmacokinetic properties should also be included as important filters in virtual screening. Here, the current development in theoretical models to predict drug absorption-related properties, such as intestinal absorption, Caco-2 permeability, and blood-brain partitioning are reviewed. The important physicochemical properties used in the prediction of drug absorption, and the relevance of predictive models in the evaluation of passive drug absorption are discussed. Recent developments in the prediction of drug absorption, especially with the application of new machine learning methods and newly developed software are also discussed. Future directions for research are outlined.Keywords: ADME, drug adsorption, permeability, Caco-2 monolayer, blood-brain partitioning (BBB), logBB, QSAR.In the traditional drug design paradigm, the central stage focuses on the activity and the specificity of a drug candidate, while some other properties, especially those related to absorption, distribution, metabolism, excretion (ADME) and even toxicity (Tox), are only considered at a later stage. The in vitro screening using the traditional strategy may usually lead to potent ligands but not necessarily good drug candidates, since lead compounds that have high molecular weight and increased lipophilicity usually tend to have high potency but poor absorption. It has been estimated that about 40%-60% of such failures are caused by ADME/Tox deficiencies [1][2][3]. The significant failure rate of drug candidates in late stage development is driving the need for development of new in vitro, in vivo, and in silico tools that can eliminate inappropriate compounds before substantial resources are wasted. Accordingly, a paradigm shift has occurred in the initial phases of drug discovery. In addition to potency and selectivity towards the biological target of interest, ADME/Tox properties of a drug are now taken into account at an early stage. Beginning in the early-to mid-1990s, many pharmaceutical companies took steps to integrate the functions of discovery and development scientists. Development scientists are involved in the early stage of the drug discovery program and provide input to in vitro and in vivo optimization process [3]. Furthermore, advances in automation technology and experimental ADME/Tox techniques, such as the Caco-2 permeability screening based on the three-day Caco-2 culture system, the metabolic stability screening using microsomes or hepatocytes, and the P450 inhibition assay, have enabled the assaying of much larger * Address correspondence to these authors at the Department of Chemistry and Biochemistry, Center for Theoretical Biological Physics, University of California at San Diego, La Jolla, CA 92093, USA; E-mail: wei-wang@ucsd.edu and College of Chemistry and Molecular Engineering, Peking ...