Know your ETFs: Inside the ecosystem

And that structure depends on a network of specialized market participants working behind the scenes.

Exchange‑traded funds (ETFs) have transformed modern investing. They trade like stocks and aim to provide diversified exposure – all while having grown into a multi‑trillion‑dollar industry. Yet despite their widespread use, many investors and advisors don't fully understand the infrastructure that makes ETFs work – particularly the specialized participants who ensure these funds trade efficiently throughout the day.

The ETF structure

Open‑ended and flexible

ETFs are structured as open‑ended funds, meaning the number of shares outstanding can expand or contract based on investor demand. This is a critical feature that distinguishes ETFs from closed‑end funds, which issue a fixed number of shares.

The open‑ended structure allows ETFs to remain liquid and trade close to the value of their underlying holdings. But maintaining that flexibility requires coordination among several key players, each with a distinct role in the ETF ecosystem.

Key players in the ETF ecosystem

Authorized participants (APs)

Authorized participants, or APs, are large financial institutions – typically broker‑dealers or market‑making firms – that have formal agreements with ETF providers to create and redeem ETF shares. APs operate in what's known as the primary market, where they transact directly with the fund.

When demand for an ETF rises, APs can assemble a basket of the fund's underlying securities (or cash) and deliver them to the ETF provider in exchange for newly created shares, usually in large blocks called creation units (often 50,000 shares or more). When demand falls, APs can return ETF shares to the provider and receive the underlying securities in exchange, removing shares from circulation.

This creation and redemption process is what allows ETF share supply to adjust dynamically. It also plays a crucial role in keeping an ETF's market price closely aligned with the value of its underlying assets.

Market makers

Market makers are trading firms that provide continuous liquidity in the secondary market – the public stock exchange where investors buy and sell ETF shares with one another. Market makers do this by posting bid and ask prices throughout the trading day, standing ready to buy shares at the bid price and sell shares at the ask price.

The difference between the bid and ask is known as the spread. Tighter spreads generally indicate higher liquidity and lower trading costs for investors. Market makers earn income from these spreads, and in return, they provide a valuable service: ensuring that investors can enter or exit positions even when natural buyer‑seller matches aren't immediately available.

Many firms act as both APs and market makers, but the functions are distinct. APs manage share supply in the primary market, while market makers facilitate trading in the secondary market.

Custodians

A custodian is a financial institution responsible for holding and safeguarding an ETF's underlying assets. The custodian ensures that the securities owned by the fund – whether stocks, bonds, or other instruments – are properly accounted for, protected, and available for settlement.

Custodians play a critical operational role, particularly during the creation and redemption process, when securities are transferred between APs and the Trust. They also support daily valuation and reporting, helping ensure transparency and regulatory compliance.

Pricing agents and administrators

Behind the scenes, pricing agents calculate the value of an ETF's underlying portfolio. At the end of each trading day, they determine the fund's net asset value (NAV) – the total value of the holdings divided by the number of shares outstanding.

Fund administrators work alongside pricing agents to handle accounting, reporting, and compliance functions. Together, they ensure that the ETF's financial data is accurate and disclosed in accordance with regulatory requirements.

How the ecosystem works together

The ETF ecosystem functions through coordination among these participants (Table 1):

This interconnected system allows ETFs to trade efficiently, stay liquid, and maintain prices that closely reflect the value of their underlying portfolios – even during periods of high trading volume or market volatility.