Dry powder inhalers (DPIs) are a widely accepted inhaled delivery dosage form, particularly in Europe, where they currently are used by a large number of patients for the delivery of medications to treat asthma and chronic obstructive pulmonary disease. The acceptance of DPIs in the United States after the slow uptake following the introduction of the Serevent Diskus in the late 1990s has been driven in large part by the enormous success in recent years of the Advair Diskus. This combination of 2 well-accepted drugs in a convenient and simple-to-use device has created an accepted standard in pulmonary delivery and disease treatment that only a few years ago could not have been anticipated. The DPI offers good patient convenience, particularly for combination therapies, and also better compliance. The design and development of any powder drug-delivery system is a highly complex task. Optimization of the choice of formulation when matched with device geometry is key. The use of particle engineering to create a formulation matched to a simple device is being explored, as is the development of active powder devices in which the device inputs the energy, making it simpler for patients to receive the correct dose. Patient interface issues are also critically important. However, one of the most important factors in pulmonary delivery from a DPI is the requirement for a good-quality aerosol, in terms of the aerosol's aerodynamic particle size, and its potential to consistently achieve the desired lung deposition in vivo.