Amongst the different techniques of characterization, porometry is probably one of the most important as directly related to the sieving effect of a porous media. This is a non - destructive method able to be performed on relatively large samples. Microscopic methods have been used with the disadvantage of giving information only on the surface observed. This is why several methods have been developed for getting access to the whole structur e of the porous media. Capillary porometry, thermos - porometry are examples of these methods extensively developed. One of the main advantages of capillary porometry method is that the information obtained is directly related to the permeability of the poro us media. Gas liquid porometry is well known but its application is limited by the high pressure needed for pores smaller than 100 nm. This is why, more recently, Liquid/liquid porometry has been developed based on the use of two immiscible fluids having s mall surface tension. By this way the measurement can be extended down to smaller pores (down to 2 nm). Capillary condensation method is an alternative way for extending the range of porometry to smaller pores. The advantages and disadvantages of these met hods will be discussed and some typical results will be presented. Pore Size Distribution should become in the future a standard characteristic of membranes in place of average of nominal pore size.