Green plants (Viridiplantae) have been impacted by environmental stress throughout their approximately 500 million years of evolution. Diverse sources of environmental pressure have shaped the adaptation, the diversification and the extinction of green plant lineages, ultimately influencing agriculture and human health. Environmental stress factors include temperature, drought, salinity, flooding, quantity and quality of light, concentration of atmospheric CO₂, soil nutrient and heavy metal content; all have been major topics for agricultural, ecological and environmental research in recent decades. Environmental stress responses in green plants have been studied for decades, using lab-based experimentation of biochemistry and genetics, physiological studies in controlled environmental facilities, field-based ecological surveys, broad phylogenetically based studies, or a combination of these approaches (Bromham, Hua, & Cardillo, 2016; De Storme & Geelen, 2014; Mizoguchi, Ichimura, & Shinozaki, 1997; Zhao et al., 2019). However, most studies are limited to a single or a small number of plant species. When and how did green plants evolve the adaptive mechanisms to respond to diverse environmental stresses? Addressing these questions will require application of advanced research tools coupled with a firm understanding of Viridiplantae morphology and evolution. This is a multi-disciplinary endeavour, combining expertise in plant systematics, phylogenetics, phylogenomics, molecular biology, physiology and ecology to decipher the underlying mechanisms (Figure 1). Below we give an overview of the content of the Special Issue of Plant, Cell & Environment on “Evolution of Environmental Stress Responses in Plants.” We will begin at a broad ecological-evolutionary scale, and then focus more on the fine scale adaptations involved in stress tolerance.