Pneumonitis or pulmonitis is a general term that refers to inflammation of lung tissue.

Pneumonia is pneumonitis combined with consolidation and exudation. Many factors can cause pneumonitis, including breathing in animal dander, aspiration (inhaling small food particles or vomit "down the wrong pipe"), and receiving radiation therapy to the chest.

Pneumonitis was listed as the one of the top 15 leading causes of death (at number 15) in the United States as of 2010, overtaking homicide, which dropped off the list. This was due to a number of factors, including an increase in the population of people over 75, for whom pneumonitis is a common cause of death.

It can be classified into acute interstitial pneumonitis, blood pneumonitis, lymphocytic interstitial pneumonitis, radiation pneumonitis, and uremic pneumonitis.