Exchanges, MTFs, OTFs And ATSs

Not every place a trade happens is legally the same kind of thing. Regulators split trading venues into distinct categories with different rules about transparency, membership, and what kinds of orders they can handle — and the labels differ between the US and Europe, which is a common source of confusion for anyone reading market-structure research across both.

The US categories

An exchange (like the NYSE or Nasdaq) is the most heavily regulated venue type: it must display quotes publicly, provide fair and open access to members, and file its rules with the SEC. An ATS, or Alternative Trading System, is a lighter-touch category covering everything else that matches buy and sell orders without being a registered exchange — this includes both lit ECNs and dark pools. ATSs register with the SEC under Regulation ATS but don't have to meet the same public-quoting and access requirements as exchanges, which is exactly why dark pools (a type of ATS) are allowed to match orders without displaying quotes beforehand.

The European categories

Under MiFID II, a Regulated Market is Europe's rough equivalent of a US exchange. An MTF (Multilateral Trading Facility) is a lighter-touch multilateral venue, similar in spirit to a US ATS — it matches multiple buyers and sellers under non-discretionary rules but with fewer formal obligations than a Regulated Market. An OTF (Organised Trading Facility), introduced specifically by MiFID II and limited to non-equity instruments like bonds and derivatives, allows the operator some discretion over how orders are matched — a meaningful difference from the MTF's strictly non-discretionary matching, reflecting that many bond and derivative markets are naturally less standardized than equities.

Why the labels keep tripping people up

Part of the confusion is that the same underlying business — a venue matching institutional orders without pre-trade transparency — gets a different legal label depending on jurisdiction and exact structure. A US dark pool is an ATS; its closest European counterpart usually operates as an MTF using a reference-price or negotiated-trade waiver, or in some cases as a systematic internaliser rather than a multilateral venue at all, because it's technically a single firm trading against clients rather than matching multiple third parties. None of these categories map onto each other one-for-one, so a research note comparing "European dark pools to American dark pools" is usually glossing over real structural differences in how each is regulated.

What this means in practice

Category	Region	Public quoting required	Operator discretion
Exchange	US	Yes	No
ATS (lit)	US	Optional	No
ATS (dark pool)	US	No	No
Regulated Market	EU	Yes	No
MTF	EU	Depends on type	No
OTF	EU	No (non-equity only)	Yes

Knowing which bucket a venue falls into tells you immediately what rules apply to it — whether it must show quotes, whether it can favor one client's order over another's, and which regulatory reporting regime it falls under — which is why market-structure research and regulatory filings lean so heavily on this taxonomy rather than venue names alone.