Systematic Internalisers

Not every trade in Europe happens on an exchange or a dark pool. A bank or trading firm can also simply fill a client's order itself, buying or selling against its own book instead of routing the order anywhere else. MiFID II gives this a formal name — systematic internaliser (SI) — and a specific rulebook, once a firm does it often enough and at enough size to cross defined activity thresholds in a given instrument.

Once a firm is classified as an SI in a stock, it takes on obligations a casual dealer wouldn't have. It must publish firm, two-sided quotes for liquid instruments up to a standard market size, so the market can see the prices it's willing to trade at before sending an order. Those quotes have to be accessible to other market participants on a non-discriminatory basis — an SI can't simply cherry-pick which counterparties get to see or hit its quotes. The SI is also bound by MiFID II's best-execution obligations, so it has to be able to show that internalizing a client's order actually gave that client as good or better a result than routing to a lit venue would have.

The SI regime effectively formalizes a trade-off that already existed informally in dealer markets: a client gets immediate execution and often price improvement over the public quote, without ever showing their order to the broader market, while the SI takes on the market risk of holding the resulting position. Regulators require the transparency and best-execution obligations specifically because that trade is happening bilaterally, off any venue's order book, where it would otherwise be invisible to everyone but the two parties involved.

Worked example. A large market-making bank internalizes enough of the flow in a liquid European stock to cross the SI thresholds. It becomes obligated to stream a firm two-way quote — say $50.02 bid / $50.04 offer for up to 5,000 shares — that any client can trade against. A client sends a 2,000-share buy order; the bank fills it at $50.04 directly from its own book rather than routing to an exchange, and must be able to demonstrate that $50.04 was at least as good as what the client would have gotten on the lit market at that moment.