“EIT waves” are globally-propagating disturbances in the solar corona that remain controversial almost twenty years since they were first observed by the Extreme ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). Although they were originally interpreted as waves, this assumption has been challenged by opposing observations from different instruments and spacecraft. Many conflicting interpretations have therefore been proposed to explain the phenomenon. The high temporal and spatial resolution observations provided by the Solar Dynamics Observatory (SDO) have revolutionised our understanding of these features and how they evolve through the solar corona. These observations have allowed the development of automated tracking algorithms and better data-driven simulations, which, combined with detailed case studies and statistical analysis of event databases, are leading to a better understanding of “EIT waves”. As a result, we are starting to move beyond a simple investigation of their physical nature, instead using them to study the corona through which they propagate. In this seminar I will discuss the theories proposed to explain “EIT waves”, placing them in the context of the observations available at the time and showing how they have been updated with improved observations and models. We then look towards the future, using a combination of ground and space-based instruments to examine how “EIT waves” may be used to study the structure of the solar corona and infer the properties of their associated coronal mass ejections.