How and when are CALL/PUT options executed if you're the seller?

External question — Personal Finance Stack Exchange Author: leigero Original post: https://money.stackexchange.com/questions/137673 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. Let's say there's a stock trading at $100 and you sell a PUT for $80 that expires the coming Friday. The stock drops to $75 by Tuesday. When are you actually forced to buy the stock? Does the option have to reach expiration date? Does the broker decide who they want to force executions on or is the very specific buyer of that option (and only them) the deciding factor? I currently hold a PUT option that is ITM for whomever bought it, and yet it has not been exercised and I'm not sure how/when or who makes the decision on exercising that option.