Non-invasive delivery systems are desirable for routine administration of therapeutic protein and peptides. The large absorptive surface area of the lungs, thin alveolar epithelial barrier, and extensive vasculature makes the pulmonary route a promising option. For many years, drug delivery to the lungs has been achieved by nebulizers and metered dose inhalers. Two rapidly expanding fields of aerosol drug delivery are liquid-spray systems and dry-powder delivery systems. The selection of an aerosolization system for protein and peptide active compounds will be driven by several inter-related factors that include: physicochemical properties of the macromolecule, the principle of aerosolization of the device, and patient- and disease-related properties. Although novel liquid spray systems may have aerosol and delivery advantages over current inhalation aerosol technologies, rigorous scientific evaluation has not yet been performed due to the relatively recent introduction of these systems. Alternatively, dry-powder inhaler systems for protein and peptide therapeutics have undergone significantly more scientific evaluation. Dry-powder systems for protein and peptide therapeutics may have stability and sterility advantages. However, with currently used excipients and passive dispersion mechanisms, these devices are relatively inefficient. A convergence of improved particle manufacturing methods and technologies with active dispersion technologies may lead to more efficient delivery options. Alongside these delivery considerations, issues pertaining to economic viability, regulatory approval, and patient factors are equally important for selection of an appropriate delivery system. Thus, with our current understanding, there is no acceptable decision tree or algorithm that can be used to derive the most appropriate device technology for inhaled protein and peptide therapy. This review aims to provide guidance to select the best formulation alternative to deliver a candidate protein/peptide drug through the pulmonary route. [ABSTRACT FROM AUTHOR]