This book aims to study the existence of the solutions of some elliptic unilateral problems in the framework of Sobolev spaces with variable exponent. One of our motivations of studing these problems comes from applications to electrorheological fluids "smart fluids", to image processing and elasticity. Under our assumptions, the problems do not admit, in general, weak solutions. To overcome this difficulty, we introduced the notion of an entropy solutions and by using the technics of monotonocity method we reached our results.