COPD is a chronic obstructive lung disease and is the third leading cause of death in the world. Inhaled corticosteroids (ICS) are one of the only treatments for COPD and are unfortunately accompanied by a number of side effects, such as an increased risk of pneumonia and hoarseness. Furthermore, treatment with ICS is less effective in some of the patients with COPD, therefore it is important to identify the reasons of corticosteroid resistance and which patients respond more favourable to treatment with ICS. In this review the influences of ICS on airway inflammation in COPD patients will be discussed, divided into long term and short term effects. In addition, the effect of cigarette smoke will be covered, which reduces histone deactelyase 2 and therefore inhibits the function of corticosteroids and eventually leads to corticosteroid resistance. Finally, the effect of treatment with ICS on gene expression will be discussed, which might be a promising start for identifying which patients show more responsiveness to treatment with ICS.