When looking at a level 2 table, we'll usually see: enter image description here

So we see 2 tables, one for bids and one for asks. For each, we see 3 columns. What I don't understand is the MMID column.

I understand that it stands for Market Maker ID. But as far as I know, a market maker is a stock exchange participant. And from these 4 letter identifiers it seems that they stand for different stock exchanges, not specific stock exchange participants.

Is there some inter-stock-exchange activity? Are there securities passing from one stock exchange to another?

Would be great if someone can elaborate.

  • 1
    What's the source for your screenshot?
    – 0xFEE1DEAD
    Commented Jun 27, 2023 at 11:34
  • 1
    Some YouTube video, why?
    – YoavKlein
    Commented Jun 27, 2023 at 11:57
  • 2
    @YoavKlein Helps determine the screenshot's credibility. Something from a low-quality website/random YouTuber could just have been thrown together with no real meaning.
    – TripeHound
    Commented Jun 27, 2023 at 14:03
  • 3
    @YoavKlein did you ask the YouTuber? Seems like a good place to start.
    – Pete B.
    Commented Jun 27, 2023 at 15:29
  • 6
    @YoavKlein comments are for requesting clarification, which is exactly what the commenters are doing.
    – Vicky
    Commented Jun 27, 2023 at 16:49

1 Answer 1


MMID is the "Market Maker Identifier", a 4-letter ID that identifies individual market makers and is assigned by FINRA (Financial Industry Regulatory Authority Inc.)

Here in this L2 table, you see the NBBO (National Best Bid and Offer) prices. Most symbols are traded at multiple exchanges, and yes you are correct that the prices are quoted by market makers at different exchanges. Just because you see the prices at different exchanges does not necessarily mean you can trade at these prices though.

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