The purpose of this study is to assess an investigational drug called etrasimod (also referred to as the “study drug”) in the treatment of Crohn’s disease (CD). This study is being done to find out which dose of etrasimod works, which is the safest dose, and how tolerable it is for people with moderate to severe CD. The study will also look at: 1. Whether etrasimod works, how safe and tolerable it is over a longer period. 2. How etrasimod affects the body (pharmacodynamics) and 3. What the body does to etrasimod (pharmacokinetics).

Your participation in the study may last for up to 74 weeks (about 1 year and 5 months). The study will have 2 treatment periods: a 14-week induction period and a further 52-week extension period. You can take part in this study if you are: 1. 18-80 Years of age; 2. Have been diagnosed with moderately to severely active CD for at least 3 months; 3. did not respond to CD therapy, responded to CD therapy at first but are no longer responding, or could not tolerate available CD therapies. You can contact any of the individuals listed below to take part in this research study.