Snowball sampling is a non-probability sampling technique used in qualitative and mixed-method research operations when a target population is too dispersed, too private, or too niche for conventional recruitment channels to reach efficiently. Researchers recruit an initial set of participants who then refer peers, colleagues, or community members who meet the study criteria, creating a chain of referrals that grows the sample organically. The method is especially valuable for research into sensitive topics, specialist professional groups, rare conditions, or subcultures where trust and social connection are prerequisites for participation. Because sample composition depends on referral networks rather than random selection, snowball sampling introduces known biases that researchers must account for during analysis and when scoping the generalisability of findings.