Obstructive respiratory diseases such as asthma feature time-variation in presence of symptoms. For example in asthma there is typically a decline in lung function during night. Due to methodological limitations of current lung function measurement methods this fundamental variation has been difficult to quantify, especially in young children and infants. In this chapter, a recently proposed wearable lung function assessment method based on impedance pneumography is presented. The physiological and technical theoretical background, and technical advancements and clinical studies are discussed. In light of current clinical information, the proposed solution may have clinical value for assessment of obstructive respiratory diseases, especially because it enables assessing lung function in a continuous real-life setting.