IEC 61300-3-29:2014 identifies two basic measurement methods for characterizing the spectral transfer functions of DWDM devices. The transfer functions are the functions of transmittance dependent of wavelengths. In this standard, optical attenuations are also used. The transfer functions can be used to produce measurements of insertion loss (IL), polarization dependent loss (PDL), isolation, centre wavelength, bandwidth (BW) and other optical performances. This second edition cancels and replaces the first edition published in 2005. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - terms and definitions have been added and reconsidered in order to be harmonized with IEC 62074-1; - characterizations of the device under test have been reviewed; - details to be specified have been reconsidered. Keywords: spectral transfer functions of DWDM devices, measurements of insertion loss (IL), polarization dependent loss (PDL), isolation, centre wavelength, bandwidth (BW).