The purpose of the current study was to develop and validate the Online Teaching Motivation Scale (OTMS), a survey instrument designed to reliably measure motivational constructs related to online teaching and learning. The widespread prevalence of online and hybrid teaching modalities, many established during the COVID-19 pandemic, has necessitated reliable, valid measures to better understand factors that impact teachers' motivation for online teaching and learning. The OTMS went through a rigorous validation process, including a pilot survey for content review, digital administration to K-12 teachers (N=379), and confirmatory factor analysis. The result was a 24-item survey designed to measure teacher motivation for online teaching based on three factors: teacher self-efficacy for online teaching, teacher perceptions of online teaching and learning, and perceived administrative support for online teaching. The OTMS was found to have a strong model fit, as well as strong reliability and validity measures. Future research includes wide administration of the OTMS to examine the relationship between K-12 teacher motivation for online teaching and students' achievement and to inform the development of appropriate support models.