Filtration processes are manifold and often critical within biopharmaceutical processes. Knowing different filter types, use, and criticalities will help to make appropriate choices of which filter should be used where, what is required to size a filter system appropriately, what to look out for and, if needed, how to troubleshoot filtration problems. Moreover, filter integrity testing is as much a key success factor of sterilizing grade filtration as the filter itself. Again, the right choice of test, when to test and what to do when a test fails are critical knowledge points within the filtration processes.