Hashtags offer exciting opportunities for professional development, teaching, and learning. However, their use reflects users' needs and desires. To illustrate and problematize the ways hashtags are used in professional development settings, this study reports on users' participation patterns, users' roles, and content contributed to three unique hashtags. This mixed methods research employs data mining techniques to retrieve data. Using a collective case study methodology, the study compares and contrasts the use of three hashtags and offers insights into the use of hashtags as emerging learning and professional development environments. Results show that hashtags exhibit similarities, such as unequal user participation. Findings also reveal differences between hashtags. For instance some hashtags are used on an ongoing basis while others have well-defined start and end dates. Ultimately, these results question deterministic thinking with respect to emerging technologies and novel professional development environments.