ETFs are securities certificates that state legal right of ownership over part of a basket of individual stock certificates. Several different kinds of financial firms are needed for ETFs to come into being, trade at prices that closely match their underlying assets, and unwind when investors no longer want them. Laying all the groundwork is the fund manager. This is the main backer behind any ETF, and they must submit a detailed plan for how the ETF will operate to be given permission by the SEC to proceed.
In theory all that a fund manager needs to do is establish clear procedures and describe precisely the composition of the ETF (which changes infrequently) to the other firms involved in ETF creation and redemption. In practice, however, only the very biggest institutional money management firms with experience in indexing tend to play this role, such as The Vanguard Group and Barclays Global Investors. They direct pension funds with enormous baskets of stocks in markets all over the world to loan stocks necessary for the creation process. They also create demand by lining up customers, either institutional or retail, to buy a newly introduced ETF.
The creation of an ETF officially begins with an authorized participant, also referred to as a market maker or specialist. Highly scrutinized for their integrity and operational competence, these middlemen assemble the appropriate basket of stocks and send them to a specially designated custodial bank for safekeeping. These baskets are normally quite large, sufficient to purchase 10,000 to 50,000 shares of the ETF in question. The custodial bank doublechecks that the basket represents the requested ETF and forwards the ETF shares on to the authorized participant. This is a so-called in-kind trade of essentially equivalent items that does not trigger capital gains for investors.