Abstract: A lateral displacement array that includes a conduit in which there is an array that includes a number of vertically asymmetrical posts that are positioned in an ordered fashion that is asymmetric with respect to the direction of liquid flow within the array such that particles of at least a critical size will be laterally displaced as they flow through the array is described. Methods for separating particles having at least a critical diameter from 16 a liquid using a lateral displacement array and a microfiltration system including a number of lateral displacement arrays are also described. Array subunits suitable for the assembly of the lateral displacement array are also described that include posts on either side of a floor that are arranged on each side with half the usual density so that when the subunits are combined a lateral displacement array with the desired array of posts is formed.