Poor water solubility for many drugs and drug candidates remains a major obstacle to their development and clinical application. It is estimated that around 40% of drugs in the pipeline cannot be delivered through the preferred route or in some cases, at all owing to poor water solubility. Conventional formulations to improve solubility suffer from low bioavailability and poor pharmacokinetics, with some carriers rendering systemic toxicities (e.g. Cremophor1 EL). To date, nanoscale systems for drug delivery have gained much interest as a way to improve the solubility problems. The reduction of drug particles into the sub-micron range leads to a significant increase in the dissolution rate and therefore enhances bioavailability. Nanosizing techniques are important tools for improving the bioavailability of water insoluble drugs. In this review, several major nanonization techniques that seek to overcome these limitations for drug solubilization are presented. Strategies including drug nanocrystals, nanoemulsions, nanosuspension and polymeric micelles are reviewed. Finally, perspectives on existing challenges and future opportunities are highlighted.