Recently I wrote a Primer (a short tutorial/introduction for a subject of broad interest) to accompany a new paper in PLoS Biology demonstrating stress-specific mutation spectra in E. coli (Maharjan and Ferenci 2017). Stress-induced mutagenesis (SIM) is a fascinating phenomenon, whereby some organisms show a transient increase in mutation rates when exposed to stresses such as starvation. However, the evolutionary implications of this phenomenon have been controversial, and I give a brief introduction to this debate (and potential ways forward) in my Primer. In their paper, Maharjan and Ferenci show that not all stresses induce mutagensis, but each stress produces a unique distribution of mutational types. These results suggest that stress-specific mutation spectra may influence evolutionary trajectories in a stress-specific manner. This remains to be explicitly tested, but we are now a little bit closer to understanding the evolutionary consequences of SIM.