A sample frame is the complete list or defined boundary of the population a research study intends to represent, forming the foundation of sound participant recruitment in qualitative and quantitative research operations. When a sample frame is poorly defined, even a well-designed discussion guide and rigorous moderation cannot save the findings, because the wrong people are answering the questions. In qualitative research, the sample frame typically combines demographic criteria, behavioral qualifiers, and category involvement to ensure participants can speak credibly to the research objectives. Getting the sample frame right before fieldwork begins is one of the most consequential decisions a research team makes, directly affecting the validity, credibility, and stakeholder confidence of every finding that follows.