We study strategic trading by a blockholder who may both monitor a firm and trades its shares over time. We study the effects of the blockholder having access to private information. In the presence of private information, the blockholder faces an illiquid market. We show that private information leads to a larger block size in good states, but might lead to a lower block size in bad states, by increasing the blockholder’s trading speed. Despite the heterogeneous impact on expected block size, and unlike in static settings, we show that private information leads to a Pareto improvement: it not only increases the stock price, and benefits small uninformed investors, but also benefits the blockholder, notwithstanding its negative impact on liquidity. We apply our model to study the optimal IPO mechanisms. We show that post-IPO trading significantly modifies the IPO design, sometimes exacerbating aftermarket volatility.