There is a bewildering array of processes that can be used for the production of thin films. A list that is certainly far from complete is given in Table 1 simply with the intention of demonstrating this fact. Many of the processes listed there have not been or are not normally used for optical purposes and so their potential is largely unknown. Those that are used are not necessarily suitable for all types of optical coatings. An exhaustive survey is impossible within the constraints of this paper and so we deal with only a few of them. We choose those that are most commonly employed together with some that although currently uncommon appear to have considerable future potential. Although this conference is aimed at excimer lasers, it would be too restrictive to limit the discussion to only those processes that have been already used for the production of excimer laser coatings. It must be recognized that much pioneering work on the processes to be described has been carried out for applications other than optics. This account is heavily biased towards optical applications and so optical references have been selected and cited wherever possible in preference to other, even prior, work.