The research aims at defining the concept of cloud computing , Its usage in general and in libraries specifically , The most important services it offers , the reasons which motivated libraries to change to the cloud , and the most famous companies and institutions working in this field . The research concluded that cloud computing has many uses which include saving the required expenditure to purchase computers and software and reducing the number of specialists responsible for system maintenance . It also has its defects represented in , information security and privacy . Electronic Arabic and English sources published on internet were used for data collecting .