Glossary term
Alternative Trading System (ATS)
An alternative trading system is an SEC-regulated electronic trading venue that matches securities orders without registering as a national exchange.
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What Is an Alternative Trading System?
An alternative trading system, or ATS, is an SEC-regulated trading venue that matches buyers and sellers of securities but is not registered as a national securities exchange. ATSs are often operated by broker-dealers and can include electronic communication networks, crossing networks, and some dark pools.
The term matters because not all securities trading happens on public exchanges such as the NYSE or Nasdaq. Some orders are matched away from exchanges through regulated venues with different transparency, access, and execution characteristics.
Key Takeaways
- An ATS is a non-exchange venue for matching securities orders.
- ATSs are regulated by the SEC and generally operate under Regulation ATS.
- Many ATSs are operated by registered broker-dealers.
- Dark pools are one type of ATS associated with less pre-trade transparency.
- Investors should care about order routing, execution quality, liquidity, and conflicts of interest.
How an ATS Works
An ATS brings together orders from buyers and sellers. Instead of displaying orders on a traditional exchange order book, the system may match orders electronically according to its own rules, subject to regulatory requirements. Some ATSs are designed for institutional block trades. Others support more automated or specialized trading.
ATSs can help market participants find liquidity, reduce market impact, or access different trading protocols. They can also raise questions about transparency, fair access, and whether customers understand where and how their orders are routed.
ATS Versus National Securities Exchange
Feature | Alternative trading system | National securities exchange |
|---|---|---|
Regulatory status | Typically broker-dealer operating under Regulation ATS | Registered exchange |
Order display | May be limited or private | Generally more public market data |
Common users | Broker-dealers, institutions, specialized participants | Broad public market participants |
Investor concern | Execution quality, routing, opacity, conflicts | Market data, liquidity, listing and trading rules |
Why It Matters
ATSs are part of modern market structure. They can improve execution in some circumstances, especially when large orders might move the displayed market. They can also fragment trading across venues, making it harder to see the full picture of supply and demand.
For retail investors, the key issue is usually indirect. Most individuals do not choose an ATS manually. Their broker routes orders across venues. That makes broker order-routing practices, payment arrangements, best execution, and trade confirmations important.
Limits and Misunderstandings
An ATS is not unregulated simply because it is not an exchange. It is subject to SEC rules and oversight. But it may not operate with the same public-facing structure as a traditional exchange.
Another misunderstanding is that dark trading is automatically harmful. Less visible trading can help some large orders avoid market impact, but it can also reduce transparency. The value depends on how the system operates and whether customers receive fair execution.
The Bottom Line
An alternative trading system is a regulated non-exchange venue for matching securities orders. It is an important part of market plumbing, but investors should understand that off-exchange trading raises practical questions about transparency, routing, execution quality, and conflicts.