This chapter discusses solid phase peptide synthesis, an idea which first appeared in a scientific publication by Merrifield in 1963. It explains why the term ‘solid phaseȉ is misleading, elaborating that the reactions do not take place in or on the surfaces of solid phases, but in gel systems produced by the penetration of solvent and solute molecules into the polymeric matrix. The chapter also reviews how solid phase methods dominate synthetic peptide research and have been extended to other fields, such as peptide sequence analysis and oligonucleotide synthesis. The chapter looks at Merrifield's description of a synthesis of bradykinin, which served as the prototype for the standard approach associated with his name. It explores Merrifield's approach, wherein polystyrene that is crosslinked by the incorporation of a small amount of divinylbenzene is chloromethylated. It also covers the Sheppard approach introduced in the 1970s