The present invention provides a fluorinated surfactant having the general formula: [R.sub.f--(O).sub.t--CQH--CF.sub.2--O].sub.n--R--G (I) wherein R.sub.f represents a partially or fully fluorinated aliphatic group optionally interrupted with one or more oxygen atoms, Q is CF.sub.3 or F, R is an aliphatic or aromatic hydrocarbon group, G represents a carboxylic or sulphonic acid or salt thereof, t is 0 or 1 and n is 1, 2 or 3. The surfactant is particularly useful in polymerizing fluorinated monomers in an aqueous emulsion polymerization.