Photonic events with missing energy have been observed 
in 189--209 GeV $\rm e^+e^-$ collisions using the OPAL detector at LEP.
Results are presented for single-photon and acoplanar-photons
event topologies. Cross-section measurements are performed and 
upper limits on cross-section times branching ratios for the class 
of new physics models $\rm e^+e^-\rightarrow XX,XY$ are derived for stable and 
invisible Y. Additional results are given for certain specific new
physics models.