The purpose of this study is to assess the safety and effectiveness of three different treatments for patients with Crohns disease who have not responded to previous treatment with a group of drugs commonly used to treat Crohn's Disease (5-ASA) and corticosteroids. Patients will receive either infliximab (a drug used to treat autoimmune diseases) or azathioprine (an immunosuppressant or drug used to suppress the immune system) or a combination of both for up to 34 weeks. This research study will involve approximately 500 patients. The main study involves up to 34 weeks (approximately 8 months). A study extension of an additional 20 weeks (approximately 5 months) is optional for patients who successfully complete the main study. A country-specific study extension of open label infliximab treatment for an additional 1 year is optional for patients who successfully complete the main study extension.