Publisher Summary This chapter discusses the preparation of pharmaceutical compounds by immobilized enzymes and cells. Immobilized enzymes and cells can be used to prepare many pharmaceutical compounds. Industrial exploitation of enzymes and microorganisms traditionally has been accomplished by using intact microorganisms or soluble cell free enzyme preparations. These processes are not very efficient because the catalysts (enzymes or microorganisms) are used for just one batch reaction or fermentation. Additional uses are not feasible because: enzymes and cells are relatively unstable and may lose activity during a fermentation or reaction; and conventional recovery methods are either expensive or cause denaturation and loss of catalytic activity. If enzymes and microorganisms are to be reused effectively, their stability must be improved, and inexpensive non-destructive recovery methods must be developed. Immobilization offers a means of achieving both objectives.