This document discusses the selection, sizing, and operation of bioprocess filtration trains for optimal performance. It covers background on membrane types used in biopharma processing including ultrafiltration, virus retentive, and microfiltration membranes. It then discusses filtration mechanisms, series filtration, and modeling approaches to predict filter performance and sizing including classical fouling models and combined blocking and adsorption models. Experimental data is presented to validate the predictive capability of the combined blocking and adsorption fouling model for sizing filters in a series configuration.