Numerical simulations of jet propagation

Astrojet simulations have been directly motivated for 20 years by the observations: from light jets to heavy jets, from hot to cold, from ionised to molecular, and adiabatic to supercooled. This is, coincidently, a sequence of increasing computational difficulty due to the increasing range of time and length scales. The progress in several directions is reviewed here, in terms of the effects of cooling, instabilities and the magnetic field. To simulate molecular jets from protostars now provides a great challenge. The contrast between physical and detectable quantities stresses the need for predicting both spectral and spatial distributions. These and some further outstanding problems are discussed.