Context: Software practitioners are a primary provider of information for field studies in software engineering. Research typically recruits practitioners through some kind of sampling. But sampling may not in itself recruit the "right" participants. Objective: To assess existing guidance on participant recruitment, and to propose and illustrate a framework for recruiting professional practitioners as credible participants in field studies of software engineering. Methods: We review existing guidelines, checklists and other advisory sources on recruiting participants for field studies. We develop a framework, partly based on our prior research and on the research of others. We search for and select three exemplar studies (a case study, an interview study and a survey study) and use those to illustrate the framework. Results: Whilst existing guidance recognises the importance of recruiting participants, there is limited guidance on how to recruit the "right" participants. The framework suggests the conceptualisation of participants as "research instruments" or, alternatively, as a sampling frame for items of interest. The exemplars suggest that at least some members of the research community are aware of the need to carefully recruit the "right" participants. Conclusions: The framework is intended to encourage researchers to think differently about the involvement of practitioners in field studies of software engineering. Also, the framework identifies a number of characteristics not explicitly addressed by existing guidelines.