Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

If I put in a limit order for the same price and size as someone else, which order goes through?
While littleadv's answer is true for many exchanges (in particular the stock market, it's called FIFO matching) you should also know that some markets trade pro rata.  That is, for a match at some price level everyone at that level gets a chunk of the deal proportional to their input (i.e. order size). E.g. match for quantity X at a price level and passive side orders y1, y2; the order y1 would get y1 / (y1 + y2) of X and y2 would get y2 / (y1 + y2)  (for X = min(X, y1 + y2)).