Phenazine dyes and their polymers are reviewed with respect to their application in electrochemical sensors and biosensors, for which they are finding increasing application as redox mediators due to their unique redox and also chromatic properties, being used for the development of (bio)sensors for direct or indirect analyte determination. Electrocatalytic effects decrease the overpotential of a number of important analytes and help increase sensitivity and decrease the detection limit, in some cases, allowing the simultaneous determination of several analytes; their properties as redox mediators can be improved when combined with carbon nanotubes. Future perspectives are indicated.