Due mainly to their poor stability and short plasma half-life, peptides are usually administered by injection, often several times daily. Injectable sustained-release formulations of peptides based on biodegradable polymer microparticles or implants early demonstrated the power of drug delivery technologies to enhance patient adherence and convenience, and increase safety and efficacy. Injectable sustained-release formulations are likely to remain a significant part of new peptide products. However, a new generation of technologies that enable solvent-free formulations and manufacturing processes, injection through narrow gauge needles and ready-to-use presentations will be increasingly used. In addition, the tremendous developments in noninvasive routes of delivery are likely to result in more and more peptides being delivered by the oral, transdermal, nasal or inhalation routes.