  A programme of worldwide, multi-wavelength electromagnetic follow-up of
sources detected by gravitational wave detectors is in place. Following the
discovery of GW150914 and GW151226, wide field imaging of their sky
localisations identified a number of candidate optical counterparts which were
then spectrally classified. The majority of candidates were found to be
supernovae at redshift ranges similar to the GW events and were thereby ruled
out as a genuine counterpart. Other candidates ruled out include AGN and solar
system objects. Given the GW sources were black hole binary mergers, the lack
of an identified electromagnetic counterpart is not surprising. However the
observations show that is it is possible to organise and execute a campaign
that can eliminate the majority of potential counterparts. Finally we note the
existence of a "classification gap" with a significant fraction of candidates
going unclassified.
