Book excerpt: Guest editor Thomas Penzel has assembled an expert team of authors on the topic of Technology to Assess Sleep. Article topics include: Sleep Apps using new sensor technologies; Sleep Apps to assess sleep quality; Pulse wave analysis; Peripheral arterial tone to assess sleep disordered breathing; Pulse transit time to assess cardiovascular function; A computer model of sleep and breathing regulation; Upper airway imaging; Quantifying leg movement disorders; Multi center sleep studies; Cardiorespiratory coupling during sleep; Quantifying airflow limitation and snoring; and more!