The Masked Gnatcatcher (Polioptila dumicola) is a small active insectivorous songbird, found in northern Argentina, Uruguay, Paraguay, Bolivia and southern and central Brazil. It is found in a wide range of semi-open habitats, including dry forest and Cerrado. It is generally fairly common, and consequently considered to be of least concern by BirdLife International and IUCN.

Its jizz is similar to that of other gnatcatchers; a small bird with a relatively long thin bill, a long frequently cocked tail, and grey upperparts. The central rectrices are black, while the outer are white (consequently, the tail appears primarily black from above, white from below), and there is a white patch in the wing (caused by broad white edging to the tertials). Males of the southern and western group (including subspecies saturata), the Masked Gnatcatchers in the strict sense, have grey underparts and a broad black mask. Females lack the mask, but instead have a black patch behind the eyes on the auriculars. The northern nominate subspecies dumicola is distinctive, with white underparts in both sexes, and a narrow black mask in the male. It may be a separate species, Berlepsch's Gnatcatcher.