As a paradigm shifting player of tissue engineering, organs-on-chips (OOCs) are considered to hold great potential for future “clinical trials on chip” as well as a step forward to design personalized medicine. Despite all ethical concerns raised by community and suspicious attitude of medical authorities, the eld keeps evolving with a remarkable speed. Although the majority of efforts have been made on making OOCs more physiologically relevant via 3D cell culture techniques, incorporation of smart biomaterial matrices and micro uidic designs, considerable amount of studies have also been focused on these providing monitoring tools to these platforms. The aim of this review is to provide, for the rst time, a comprehensive report on already available methods for monitoring OOCs. In that regard, this paper critically reviews physical, chemical and biochemical sensors that have been implemented for OOCs and cell culture monitoring by also discussing the advantages and disadvantages associated with each proposed method.