This study is exploring the safety of combining **elranatamab** and **iberdomide** for treating **relapsed or refractory multiple myeloma**. Multiple myeloma is a cancer affecting white blood cells that produce antibodies. "Relapsed" means the cancer has returned after getting better, and "refractory" means it doesn't respond to treatment. The study has two parts. **Part 1** checks safety and tolerance, while **Part 2** finds the right dosage. Participants receive elranatamab as an injection and take iberdomide pills for 21 days in a 28-day cycle. Participants remain in the study until the disease worsens, side effects become too severe, or they choose to leave. The goal is to determine if these medicines are safe and effective for treating multiple myeloma. **Key Points:** - The study involves taking medicine every 28 days. - Participants will stay in the study until their disease changes or they decide to stop. - The study aims to find a safe and effective treatment for multiple myeloma. **Eligibility:** Patients must have a history of multiple myeloma with specific measurable criteria. Certain health conditions and past treatments may disqualify participation.