Abstract This paper provides a guide to linguistic fieldworkers for identifying, documenting, and describing sound segments that may be marginal in a language's phonological system. The main contribution of this study is a detailed discussion of linguistic fieldwork methods for investigating different factors that may influence phonological marginality. A proposed scale helps assess a presumed contrast's relative position on a continuum of marginality. Each factor's possible impacts on a sound's marginality are discussed, and a holistic approach is proposed. This guide is mostly aimed at fieldworkers working with lesser-documented languages, and the emphasis is on practical application rather than theoretical modelling.