Oral drug delivery systems being the most cost-effective and leads the worldwide drug delivery market. The major problem in oral drug system is low and erratic bioavailability, which mainly results from poor aqueous solubility. This may lead to high inter and intra subject variability, lack of dose proportionality and therapeutic failure. For the improvement of bio-availability of drugs with such properties presents one of the greatest challenges in drug formulations. Various technological strategies are reported in the literature including solid dispersions, cyclodextrines complex formation and micronization. Including these approaches self-emulsifying drug delivery system (SEDDS) has gained more attention for enhancement of oral bio-availability with reduction in dose. SEDDS are isotropic mixtures of oil, surfactants, solvents and co-solvents/surfactants. For lipophilic drugs, which have dissolution rate-limited absorption, SEDDS may be a promising strategy to improve the rate and extent of oral absorption. This book explains how self-emulsifying drug delivery systems can increase the solubility and bioavailability of poorly soluble drug.