The preservice preparation and ongoing professional development for instructors of adult emergent bi/multilingual learners (EBLs) in the United States has been characterized as "deeply uneven," lacking uniformity, consistent academic rigor, and practical application to bolster instructors' feelings of self-efficacy and agency in addressing their students' complex learning needs. Using the "Standards for ESL/EFL Teachers of Adults" (2008) as a foundation, this explanatory sequential mixed methods research study explored the reflections of instructors of adult EBLs regarding their preservice preparation, ongoing professional development, and the guidance and support received from teaching colleagues and supervisors. The survey instrument developed contained a combination of demographic and open-ended questions and Likert scale sub-surveys, one focusing on preservice preparation and another on collegial and supervisory support. Unfortunately, the response rate for the survey instrument did not yield sufficient statistical power to make assertions based on the quantitative analyses conducted, but comparisons between the survey responses and the follow-up interviews suggested that participants felt adequately prepared to teach adult EBLs but could identify areas that should be modified and expanded. The follow-up interviews with 10 purposefully sampled volunteers yielded richer findings that not only identified specific topics that should be components of preservice preparation and ongoing professional development but also areas for future research. [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.]