Pulmonary drug delivery has gained significant attention as an efficient route for both local and systemic therapy. This chapter provides an overview of the respiratory system, describing its structure and function in drug absorption. The advantages of pulmonary drug delivery, including rapid onset of action, reduced systemic side effects, and noninvasive administration, are discussed. Aerosol administration is a key strategy for pulmonary drug delivery, and this chapter examines the mechanisms of aerosol deposition, factors influencing drug absorption, and methods for characterizing aerosols. Given the challenges associated with traditional drug formulations, nanocrystals have emerged as a promising approach to enhance drug solubility, dissolution rate, and bioavailability in pulmonary applications. Nanocrystals can be formulated as either liquid nanosuspensions or solid-state nanocrystals, each offering unique advantages for inhalation therapy. The chapter discusses the formulation strategies, stability considerations, and translational potential of these nanocrystal-based systems in improving pulmonary drug delivery.