Our research is focused on iPS cell reprogramming, a method that allows for the creation of patient-specific pluripotent stem cells with great potential for regenerative medicine. The process of iPS cell reprogramming is long (> 2 weeks) and inefficient (<1%), and therefore time course analysis at the single cell level single cell level is required to identify and characterize the minority population of successfully reprogramming cells. In the past year, we have leveraged the power of high-dimensional single cell analysis to map the transitions that occur during cellular reprogramming. We have identified a key intermediate stage of cellular reprogramming, and we have isolated and characterized this key intermediate population. We have also identified a late-stage non-productive reprogramming trajectory, and characterized the cellular signaling requirements for successful reprogramming to the pluripotent state. We anticipate that this work will lead to improved reprogramming protocols that produce enriched, higher-quality pluripotent stem cells for use in regenerative therapy.