We present a study of absolute instability in liquid jets paying particular attention to curved jets formed in the industrial process of prilling. We illustrate the different types of break-up modes identified in experiments on curved jets and also explain the mathematical model used to describe them. Using this mathematical model, we study absolute instability in curved jets undergoing Mode 4 type break-up. The study is extended by including the effects of the density ratio of the liquid to the surrounding gas and gravity. We carry out an experimental study on curved liquid jets concentrating on the Mode 4 break-up regime. Our theoretical results are compared with experiments and very good agreement is found between the two. In addition, we examine absolute instability in thin ligaments that are formed as the jet approaches break-up. This study indicates that the jet undergoes a local absolute instability at pinch-off around its break-up point. A brief investigation of absolute instability in curved non-Newtonian jets is also carried out finding parameters corresponding to convective and absolute instabilities. We also look at jets on very small scales (having radius of the order of micrometers and nanometers) using the interface formation model. The results obtained by using the interface formation model are compared to the classical continuum model and molecular dynamics simulations.