There are 3 separate studies being described in this form. All 3 studies have the same primary purposes, but there are some small differences between GALAXI 1 (which is a Phase 2 study) and GALAXI 2 & 3 (which are identical Phase 3 studies). Your study doctor will tell you which study you will be taking part in. The main purpose for all 3 studies (GALAXI 1, 2, & 3) is to see if guselkumab is useful for treating patients with Crohn’s Disease. The safety of guselkumab will also be studied. Another purpose of GALAXI 1 is: To find the dose of guselkumab that would be best to use in future studies (such as GALAXI 2 & 3) for the treatment of Crohn’s Disease. A dose is a measured amount of a drug taken at one time. Another purpose of GALAXI 2/3 is: To find the dose of guselkumab that best treats Crohn’s Disease. The effects on Crohn’s Disease as well as any side effects will be explored, and to compare the effects (both good and bad) of guselkumab to those of ustekinumab and placebo (placebo looks just like guselkumab and ustekinumab and is given the same way but has no active drug in it).