The ability to model behind armour debris (BAD) is important in assessment of vulnerability and lethality. It is very hard to find a suitable model, despite the well recognized importance of the phenomena. A literature review of models and simulations of BAD is presented together with a short description of some hydrocodes and important concepts in numerical simulations. Many physical, empirical and statistical models handle only part of the problem; either target failure or BAD cloud characteristics. Numerical simulations have problems with fracturing of the target material. Numerical erosion is sometimes used to assess which computational cells that form BAD. The numerical simulations are often combined with a post processor to include the stochastic behaviour of the debris cloud. It is concluded that this is a research field that still needs a lot of work, both experimentally and numerically, before the models are reliable and usable in or as pre-processors to vulnerability assessment.