This study will compare the absolute and relative effectiveness of managing real-life asthma with and without the use of NIOX MINO® and NIOX Flex® to measure exhaled nitric oxide (eNO) as a marker of underlying airway inflammation to guide appropriate management. As exhaled nitric oxide responds rapidly to environmental changes and can act as a marker of underlying inflammation it is proposed that incorporating eNO monitoring into routine asthma management treatment allows strategies to be more accurately tailored to the patients needs, increasing the probability of good asthma control.