This chapter introduces two major regenerated cellulose fibers, viscose rayon and lyocell rayon, as well as cellulose-derived acetate fiber. A brief history of technology development for these fibers is reviewed. Fiber manufacturing principle, physical and mechanical properties, and apparel end uses are discussed. As an example for apparel application, a case study in wedding gown design using viscose rayon fiber is presented. The chapter is concluded with a future trend of developing new regenerated cellulose fibers as green fibers featuring eco-friendly manufacture, functionalities, and energy efficiency.