This doctoral dissertation examines the relationship between teacher's professional identity and innovative work behavior in 21st century Private Catholic schools. This mixed-methods study uses a quantitative validation model which includes scale items measured on a 4-point Likert scale as well as open-ended survey questions which serve as qualitative data to support, negate, verify, and/or further explain quantitative data collected. Using an adapted Teacher Professional Identity Scale derived from validated scales which measure each of the six domains of teacher professional identity that includes items from Geisel et al. (2001); Tschannen-Moran & Hoy, (2001); Hasinoff and Mandzuk (2005); Abu-Alruz and Khasawneh (2013)); Obunadike, (2013); Hanna et al. (2020) and Lambriex-Schmitz et al.'s (2020) Innovative Work Behavior Scale, the researcher examined the relationship between six internal domains of teachers' professional identity and teachers' innovative work behavior. Data were analyzed through the lens of Rogers' (2003) Diffusion of Innovations Theory to determine which internal factors of teachers' professional identity most influence participants category of innovation adoption as set forth by Rogers (2003).Upon gaining consent from school leadership, this study surveyed 1275 teachers from 20 Private Catholic schools from Lasallian Districts within the United States. The research outcomes of this study provide insight into ways educational leadership can streamline the diffusion of innovations in educational organizations to meet the needs of both teachers and students in the 21st century. Understanding teacher identity in relationship to teacher innovative work behavior will assist the leadership decision making processes relating to policy and technological change fostering a higher success rate of both teacher participation and student achievement. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]