Instructional designers and professional trainers conduct many different types of training. However, some topics are job- and- task-specific and are more effectively taught by subject matter expert (SME) trainers. In some cases, these SMEs are given training and/or instructional design (ID) resources, and in other cases they have to learn best practices for instruction from trial and error and personal experience. This grounded theory study was undertaken to find out the current state of the industry for SME trainers and to isolate and discuss the skills and knowledge needed when SMEs conduct training. There was extensive literature on the nature of expertise and best practices for conducting training. Of specific note to this topic is the concept of pedagogical content knowledge (PCK). According to Shulman (1986), PCK works alongside subject matter knowledge when conducting training. Because experts and novices perceive tasks differently (Bransford et al., 2000; Dreyfus, 2004), experts who train have to be able to understand their task through the perception of the novice they are teaching, creating rules and steps to follow for the novice to progress toward expertise. There seems to be a gap in the literature regarding the PCK and effectiveness of SMEs as trainers. This study was performed by interviewing 12 SMEs who train others in their specialty and analyzing their responses using grounded theory methodology to identify the type and amount of PCK needed by SME trainers and what tools or guidance these SMEs were given to gain their knowledge. The questions reviewed participant experience and instructional practices, beliefs regarding self-efficacy and best practices for training their specialty and learners, and training or assistance received when designing and conducting training. The study found that the trainers interviewed were successful in their training tasks, since all had completed multiple training instances and were in the process of conducting more at the time of the interviews. Not all of them used the tools and tricks available to them, and many of them had to create their training program without training or guidance. Coding and comparing their answers found that those who were very experienced trainers or who had received a trainer course in their specialist topic had more robust and well-designed training programs. Those who received little or no training and were not as experienced tended to struggle a bit more. Based on their general responses and some targeted interview items, their perceived competencies were compared to the International Board of Standards for Training, Performance, and Instruction (IBSTPI) instructor competencies (2021). All participants demonstrated some competencies, and many of the participants demonstrated nine or more of the 19 competencies. Demonstrated competencies tended to follow either long experience in training or professional assistance in the form of instructional design (ID) or train-the-trainer (TTT). The conclusion reached was that SMEs can make excellent instructors, they do not typically receive training or guidance to teach, and they all would benefit from ID help and TTT or adult learning methods instruction. Implications for ID contributions in SME training contexts and future research are discussed. [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.]