The American Stock Exchange and the NMS Framework: A Complete Guide

Introduction

The American Stock Exchange is one of the most influential exchanges in the world. It perfectly captures the spirit of American financial innovation. The other big component, the National Market System (NMS), is a regulatory framework that assures that U.S. stock markets are fair, transparent, and efficient to all investors.

In addition, studying the history and development of the American Stock Exchange in conjunction with the NMS framework will give investors and financial advisors a better understanding of how markets actually work.

The American Stock Exchange: From Curbstone to Electronic

Humble Origins

The American Stock Exchange began trading in securities in New York City in the late 18th century, when stockbrokers were known as "curbstone brokers" and specialized in emerging industries and smaller companies that could not be listed on the more reputable New York Stock Exchange.

In the 1830s, those traders primarily dealt in the stocks of newly created companies such as turnpikes, canals, and railroads. The California Gold Rush of the 1840s and the discovery of oil in Pennsylvania in 1859 further expanded the curb market

Formalization and Growth

The New York Curb Market Agency opened its doors in 1908 and sought to standardise trading and promote fair play. The market moved indoors on June 27, 1921, into a new building at 86 Trinity Place in lower Manhattan. By 1929, the New York Curb Market had become the New York Curb Exchange with its own trading floor and rules.

A Pioneer in Financial Innovation

AMEX became known more than just for being a home for small companies – it was also a genuine innovator of financial products. ETFs were started in 1989 by Index Participation Shares, an S&P 500 proxy that traded on the American Stock Exchange and the Philadelphia Stock Exchange. The product was quickly discontinued, but the AMEX carried on. Nathan Most and Steven Bloom developed Standard & Poor's Depositary Receipts (SPY) under the guidance of Ivers Riley. Known as SPDRs or Spiders, the fund became the largest ETF in the world.

Mergers, Rebranding, and the Modern Era

In 1998, the AMEX merged with the National Association of Securities Dealers to create "The Nasdaq-Amex Market Group," though it regained independence in 2004. In January 2008, NYSE Euronext announced its acquisition of the AMEX, enhancing its position in U.S. options, ETFs, and cash equities.

NYSE Euronext completed the acquisition of the AMEX for $260 million in stock in October 2008. The exchange underwent several rebranding exercises over the following years, eventually settling on the name NYSE American in 2017, when it also introduced a 350-microsecond delay in trading a "speed bump" to level the playing field between high-frequency and traditional traders.

Today, NYSE American is an exchange designed for growing companies. It blends features derived from the NYSE, such as electronic Designated Market Makers (e-DMMs) with quoting obligations for each listed company, with NYSE Arca's fully electronic price/time priority execution model.

The National Market System (NMS) Framework

What Is the NMS?

The National Market System (NMS) is a regulatory mechanism that governs the operations of securities trading in the United States. It covers all entities and facilities, both public and private, that are involved in the buying and selling of stocks, including stock exchanges, trade clearinghouses, and market price quotation providers.

The NMS was created by an act of the U.S. Congress in 1975 through the Securities Act Amendments of 1975. Its basic purpose is to help ensure a level playing field for all equity investors.

Before its creation, equity markets were fragmented and opaque. No consolidated data feeds existed to ensure uniform stock price quotations across all trading exchanges in the United States, meaning some traders would receive more favourable pricing than others.

The Five Core Goals

The NMS framework operates around five core responsibilities:

1. Fair Market Competition – ensuring no single exchange dominates or disadvantages others.
2. Price Transparency – making current bids and asking prices publicly available to all market participants.
3. Best Execution – requiring that orders be filled at the best available price across all exchanges.
4. Direct Order Matching – facilitating the direct matching of buy and sell orders without unnecessary dealer intermediation.
5. Consolidated Market Data - ensuring all price and volume information is collected and distributed uniformly.

Regulation NMS (2005): The Modern Update

The regulatory framework evolved significantly through Regulation NMS in 2005, which updated the original 1975 structure to address technological advances and market fragmentation.

The 2005 update primarily aimed at lowering market data and quotation access fees in order to make current bid and ask price quotations more freely available to all equity traders. The new rules also required increased consolidation of price quotes between different trading exchanges.

One of the most discussed provisions is the trade-through rule. This rule states that an order entered on one trading exchange must be executed on a different exchange if doing so offers the investor a better price. While protective of investors' financial interests, critics have argued it slows execution for those who prioritise speed over price.

NMS Plans: The Operational Architecture

The NMS framework operates through a series of formal plans that govern specific aspects of market infrastructure:

• The CTA/CQ Plans govern the collection, processing, and distribution of quotation and transaction information for exchange-listed securities. Under these plans, all U.S. exchanges and associations that quote and trade exchange-listed securities must provide their data to a centralised securities information processor (SIP) for consolidation and dissemination.
• The LULD Plan addresses volatility. This plan governs the establishment, operation and administration of a market-wide limit-up, limit-down mechanism intended to address extraordinary market volatility in NMS stocks. It sets forth requirements designed to prevent trades from occurring outside of specified price bands.
• The CAT Plan ensures regulatory accountability. It implements Exchange Act Rule 613, calling for the creation of a single comprehensive database that enables regulators to more efficiently track all trading activity in U.S. equity and options markets.
• The CT Plan, the most recent major development, was approved in November 2024. This new NMS Plan governs the public dissemination of real-time consolidated equity market data for NMS stocks, with participants having until April 2027 to implement it, at which point the older CTA/CQ and UTP plans will cease to operate.

The Intersection: AMEX, NYSE American, and the NMS

The American Stock Exchange's evolution is deeply intertwined with the NMS framework. From its early days as a loosely regulated curb market to its current identity as NYSE American, the exchange has had to continuously adapt to the evolving regulatory landscape that the NMS defines.

NYSE American today trades in all 8,000+ NMS securities in a fully electronic manner, including electronic auctions in NYSE American-listed securities, and offers discretionary pegged orders that peg to the near side of the protected best bid and offer. This means it is not merely a passive participant in the NMS; it is one of its active pillars.

The AMEX's long association with small-cap and emerging stocks aligns with the NMS's mission of inclusivity and fair market access. Securities exchanges act as a single point of entry, exit, and re-entry for securities listed on them, as well as a point of capital raising, by allowing firms to raise capital through public offerings and liquidity for investors.

Criticisms and Ongoing Debates

Of course, no regulation is without its critics. Rules requiring that all bids and offers on any stock are publicly available have led to "dark pools", which are private trading exchanges through which large institutional investors hide their trades until they are executed. In short, the rules designed to promote more transparency in the markets have actually led to less transparency in some areas.

Further, the NMS framework continues to evolve in light of technological change caused by the rise of high-frequency trading (HFT) and the need for regulators to rethink their protections against speed and fairness, as NYSE American did recently with a trading speed bump.

Conclusion

The American Stock Exchange (NYSE American) is more than a footnote in financial history. It’s the birthplace of the modern ETF industry, a champion of small and mid-cap companies, and a living example of how markets evolve over time. The NMS architecture protects those markets.

Together, they represent two sides of the same coin: the spirit of innovation in finance and regulatory discipline required to promote that innovation. Understanding these two elements is key to understanding the new U.S. equity landscape.