Microdroplets are widely used for industrial applications such as food, drug, biotechnology and new materials. This review will summarise the key development in microdrop technologies, especially double-emulsion droplet technologies, with a focus on microchip-based techniques. For completeness, the key topics in single emulsion droplets such as generation, control and application will be briefly presented first. Then the current microfluidic techniques for double emulsion generation will be reviewed. Several techniques for increasing the instability of double emulsions are discussed, followed by methods for measuring double emulsion properties such as stability, size and mass transfer between phases. Double emulsions have found use in many biomolecular applications that include drug delivery and protein engineering. A range of methods, e.g. liposomes, polymerosomes, polymer beads and colloidosomes-based emulsions, have been developed for drug delivery applications. The future work in the area would be the development of novel partition system that encloses the chemicals and biologicals effectively and novel control mechanism for advanced sorting and selection of droplets.