Multiple sources of influence impact the decisions about what and how teacher educators are expected to operate, including the innovations that are adopted. Some of those sources of influence (such as teacher certification boards) can demand that certain curricula be adopted, specific instructional procedures be utilized, and delineate the conditions under which candidates will be selected for entry into teacher education programs. Other sources of influence include how other professionals are prepared. In this article, the authors hope to show that the types of innovation in teacher education, as well as methodologies to study impact of innovation, continue to show variety and ingenuity. The authors: (1) summarize the definitions extant in the literature; (2) briefly describe several taxonomies for innovation; (3) explain the process of innovation; (4) explicate the challenges in assessing innovation; and (5) discuss the implications for teacher education research and practice.