Alternative Trading Systems (ATS) are private trading venues that offer a platform for trading a variety of securities outside traditional exchanges. The most common types of securities traded on ATSs include equities, bonds, and derivatives.

Equities, particularly those of large-cap and mid-cap companies, are the most frequently traded securities on ATSs. These platforms attract institutional investors who are often looking to execute large block trades discreetly, away from the public eye, to avoid impacting the market price.

Corporate bonds are another common type of security traded on ATSs. The bond market benefits from ATSs as they provide a venue for institutional investors to trade large quantities of debt instruments, which might not be as liquid on traditional exchanges.

Derivatives, including options and futures, are also traded on ATSs. These instruments allow investors to hedge their portfolios or speculate on price movements. ATSs provide an alternative to the centralized derivatives exchanges, offering greater flexibility and often lower transaction costs.

Additionally, Exchange-Traded Funds (ETFs) and other pooled investment vehicles are traded on ATSs, giving investors access to a diverse set of assets. The anonymity and lower impact on market prices are key reasons these securities are commonly traded on ATS platforms.