The day has arrived; you’ve painstakingly cared for your packaging cell line, prepped your DNA, transfected and harvested your lentivirus. Now it’s time to move ahead with your infection and make your stable cell line. While we’ve all experienced the pressure to move a project forward, transductions should not be rushed into. Before you start any transduction, you should always titer your virus - that is, determine the amount of virus you actually have in your prep. Taking time to properly titer your virus will not only ensure that your infection is designed in the best possible way, but it may also save you time in the long run. Read on for an overview of the titering options as well as the benefits and drawbacks of different methods (for comprehensive protocols for all of the methods discussed here refer to Kutner et. al.).