On one side ,drying technology is a major energy cosumer used in many industries including :agriculture, biotechnology ,food ,textile mineral ,pharmaceutical,pulp and paper ,ploymer wood and other.It is also perhaps the oldest chemical engineering unit operation.Drying aims at reducing the moisture content within a product by application of thermal energy to produce dried products of desierd attributes. Control of dryers was mainly manual in the early days ;automatic control appeared only more recently in indstrial drying equipment ,especially with the introduction of PID cpntrol (the dirst paradigm in control) in 1942 by Ziegler and Nichols ,Whereas  control techniques have been widely used since the middle of the 1970's in the chemical industry,the number of applications of control in drying is still relatively , and with the complexities  of transport phenomena involved in drying ,no single controller can be applied to all dryers .Morever most of the research is still focused on the understanding of the drying mechanisms and and products quality rather than on control of the operation itself ,Therefore ,it is  not surprising to see that relatively few published works deal with control aspects in drying .In the meantime one has  to note that the major cost of dryers is not very important and that with deeper understanding of the drying ,new "smart" dryers can be made more reliable and more cost-effective  than calssical dryers.