We develop a financial market trading model in the tradition of Glosten and Milgrom (1985) that allows us to incorporate nontrivial volume. We observe that in this model price volatility is positively related to the trading volume and to the absolute value of the net order flow (i.e., the order imbalance). Moreover, higher volume leads to higher order imbalances. These findings are consistent with well-established empirical findings. Our model further predicts that higher trader participation and systematic improvements in the quality of traders’ information lead to higher volume, larger order imbalances, lower market depth, shorter duration, and higher price volatility.

In a dynamic model of financial market trading multiple heterogeneously informed traders choose when to place orders. Better informed traders trade immediately, worse informed delay – even though they expect the market to move against them. This behavior generates intraday patterns with decreasing spreads, decreasing probability of informed trading (PIN), and increasing volume. We predict that policies that foster market entry improve the welfare of uninformed traders and lead to increased market participation by incumbent traders. Technological advances that lead to better signal processing also encourage market participation and increase volume but at the expense of uninformed traders’ welfare.

Facing increased competition over the last decade, many stock exchanges changed their trading fees to maker‐taker pricing, an incentive scheme that rewards liquidity suppliers and charges liquidity demanders. Using a change in trading fees on the Toronto Stock Exchange, we study whether and why the breakdown of trading fees between liquidity demanders and suppliers matters. Posted quotes adjust after the change in fee composition, but the transaction costs for liquidity demanders remain unaffected once fees are taken into account. However, as posted bid‐ask spreads decline, traders (particularly retail) use aggressive orders more frequently, and adverse selection costs decrease.

We examine the impact of a rule in the Canadian equities market that requires dark orders to offer price improvement over displayed orders. We show that this rule eliminated intermediation of retail orders in the dark and shifted retail orders onto the lit market with the lowest trading fee. Intermediaries shifted liquidity supply to this market leading to increased displayed liquidity. We conclude that reducing retail order segmentation enhances lit liquidity. Despite the improvement in liquidity, retail traders receive less price improvement. Retail brokers pay higher trading fees to exchanges, and high-frequency traders earn higher revenues from trading fees.