Analysis of breath condensate is an innovative approach to biochemical information from the lung. It provides a new tool to estimate and characterize the burden of oxidative and inflammatory processes in the airways/lung. Clinical applications in asthma, COPD and CF can be envisioned as well as determining organ-specific inflammation in mechanically ventilated patients or monitoring patients with transplanted lungs. However, besides inflammation other important areas have begun to be evaluated, such as the demonstration of p53 mutations in NSCLC patients or an increased ratio of EBC nitrite to tidal volume in mechanically stressed lungs. Of course a careful validation of each and every parameter is paramount to the use in clinical applications. The comparison to BAL is oftentimes called for but at the same time is not the comparison to a gold standard because of the well-known problems of BAL. The scope of this review is a summary of facts and theories concerning exhaled breath condensate generation, collection and analysis but at the same time the representation of the many aspects that remain to be resolved.