In this mixed methods study, we analyzed survey and interview data from 100 preservice secondary science and mathematics teachers enrolled in four teacher education programs (TEPs) to investigate their readiness to teach multilingual learners. We defined readiness as preservice teachers' sense of preparedness to teach multilingual learners and their understanding of effective multilingual learner instruction. We examined participants' self-reported levels of preparedness, their understanding of effective multilingual learner instruction, and sources contributing to and/or limiting their readiness. We found that participants' readiness to teach multilingual learners significantly increased between the beginning and end of their TEPs. We also found that participants' understanding of effective multilingual learner instruction was significantly associated with a higher sense of preparedness. Furthermore, we found that participants enrolled in graduate TEPs reported higher levels of preparedness than participants enrolled in an undergraduate TEP. Likewise, participants whose first language was other than or in addition to English reported higher levels of preparedness. Finally, participants identified field placement experiences, personal and professional background, and coursework as factors contributing to their readiness to teach multilingual learners. We close with recommendations for teacher educators intent on helping preservice teachers better understand and implement effective instruction for multilingual learners.