IEC 61977:2015 applies to the family of fibre optic filters. These components have all of the following general features:- they are passive for the reason that they contain no optoelectronic or other transducing elements which can process the optical signal launched into the input port;- they modify the spectral intensity distribution in order to select some wavelengths and inhibit others;- they are fixed, i.e. the modification of the spectral intensity distribution is fixed and cannot be tuned;- they have input and output ports or a common port (having both functions of input and output) for the transmission of optical power; - the ports are optical fibre or optical fibre connectors;- they differ according to their characteristics.They can be divided into the following categories:- short-wave pass (only wavelengths lower than or equal to a specified value are passed);- long-wave pass (only wavelengths greater than or equal to a specified value are passed);- band-pass (only an optical window is allowed);- notch (only an optical window is inhibited).It is also possible to have a combination of the above categories. This standard establishes uniform requirements for the following: optical, mechanical and environmental properties. This third edition cancels and replaces the second edition published in 2010. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:- harmonization of a number of terms and definitions with other generic specifications;- deletion of the quality assessment level clause. Keywords: fibre optic filters generic specification