Inspiratory muscle training (IM training) is a technique that is designed to improve the performance of the respiratory muscles (RMs) that may be impaired in a variety of conditions. Interest in IM training has expanded over the past two decades, and IM training has been used in an increasingly wide range of clinical conditions. However, the benefits of IM training continue to be debated, primarily because of methodological limitations of studies conducted to date. The focus of this article is to provide a critical review of IM training research in conditions other than chronic obstructive pulmonary disease for which it has been used, including asthma, bronchiectasis, cystic fibrosis, pre- and postsurgery, ventilator weaning, neuromuscular diseases, and chronic heart failure. Emphasis is placed on what has been learned, remaining questions, future applications, and significance to practice.