ASCOS (Advanced Study Course on Optical Chemical Sensors) is a European initiative to establish an education, discussion and contact platform for young researchers working in the strongly growing field of optical chemical sensors, besides the traditional conferences. ASCOS is being held as a biennial event, each time in a different European country. To guarantee the most efficient study, ASCOS combines tutorial lectures, covering the basics of optical chemical sensors and important related fields, and group work projects, in which mixed groups of ASCOS students will be assigned a (bio)analytical problem related to optical sensors.