Various methods for sampling natural cloud droplets are reviewed with particular reference to their suitability for use on aircraft. For convenience the methods are divided into two categories: impaction sampling and optical sampling. The older methods, which are still in use, involve the impaction of water droplets on suitably prepared targets. Such targets may capture the droplets in an oil coating or many replicate the droplets by means of pits in a soot coating. The droplet spectrum may be determined by examining the targets of pits in a soot coating. The droplet spectrum may be determined by examining the targets under a microscope. Within the past decade and a half, optical methods have been developed to replace the impaction methods. These methods, notably those involving scattering or diffraction, allow large numbers of droplets to be sized in much less time than is possible with the impaction methods. (Author).