This systematic review article celebrates the 20th anniversary of hyperscanning research by examining the state of the scientific methodologies and findings. In 2002, Montague et al. proposed hyperscanning as a new method for studying human social cognition using fMRI. Ten years later, Cui et al. (2012) introduced fNIRS as a motion-tolerant device that was well- suited for hyperscanning research, especially interpersonal neural synchrony (INS). Though still in its infancy, INS research has gained notoriety, credibility, and momentum since these milestone publications. The best practices and frequent findings in INS research are still emerging. To capture the state of the science, original INS research articles (N=107) published between 2002-2022 were reviewed for study sample characteristics, experimental methods and cognitive domains, data processing and analysis approaches, as well as reported INS findings. A picture of INS hyperscanning research conventions and general findings emerge as outcome of this review.