In about a week, one of the most significant shifts in crypto’s history will happen when the blockchain Ethereum completes a software update known as “the merge.”

The merge, which is tentatively scheduled for Sept. 15, will drastically reduce Ethereum’s energy usage, making it much more environmentally-friendly than Bitcoin. The merge could also have a slew of far-reaching effects, for better or worse: it could crash or turbocharge the price of Ether; spur mainstream adoption or reduce confidence in crypto; lessen some security risks, or exacerbate others. Here’s what a layperson should know about the transition.