Michael Ludkovski University of California, Santa Barbara (UC Santa Barbara) I will discuss an ongoing project to document and model the links between order flows and execution costs. The concept of book resiliency or liquidity has been central to many popular execution models but remains elusive and ill quantified. I will present some empirical and statistical investigations related to features of executed and limit orders over time as captured by the Nasdaq LOB message tape. This provides new insights into the meso-scale of book dynamics, especially the inter-dependence between price impact, limit orders, and market order arrivals. The second half of the talk will introduce one resulting attempt at incorporating such order flow dynamics into the Almgren-Chriss execution framework.