This project contains a brief review of the giant magnetoresistance in ferromagneticrncrystals, the transport properties of ferromagnets with a brief discussion of magneticrnproperties of crystals such as magnetization susceptibility, diamagnetism, paramag-rnnetism, and ferromagnetism as well as the magnetization dynamics in ferromagneticrnsystems. Giant magnetoresistance materials have magneto transport properties whichrndetermine their suitability for applications in magnetic eld sensors, read heads, ran-rndom access memories. The discovery of giant magnetoresistance has been a hugernimpact on our life, especially for mass data storage devices. Details of giant magne-rntoresistance applications, such as hard-disk read-heads, sensors and magnetic memoryrnchips are presented. One of the important aspects of giant magnetoresistance discov-rnery was that it was immediately turned into commercially available products withrna giant market share. The highest storage capacity in the modern computers is at-rntributed to the discovery of giant magnetoresistance. This review covered a simplernmodel of giant magnetoresistance and dependence of it on structure and magneticrnlayer thickness with a brief discussion of interlayer exchange coupling and giant mag-rnnetoresistance in magnetic multilayers including the giant magnetoresistance e ect inrnferromagnets (organic semi-conductors)