Heatwaves impose disastrous impacts over human, natural and industrial systems across the globe. Over a relatively short period of time, there has been considerable advancement in the scientific understanding of heatwaves. Such advancements include how heatwaves are measured, their driving mechanisms, observed and projected changes, and quantifying the anthropogenic influence behind these changes. This paper reviews these developments. There are however gaps in the scientific literature that should be filled in order to gain a more complete understanding of the changing nature of heatwaves. The conclusions of this paper propose that the global community should work toward a unified framework in which to measure heatwaves, reduce spatial and temporal gaps by increasing the global observation network, further research on how physical mechanisms interact for heatwave manifestation, and continual work and expansion of methods used for attribution studies on observed heatwaves and their trends.