This study explores the quenching of the dianionic fluorescent whitening agent, NFW, by various substances, including methyl viologen (MV), in water and in the presence of Beta-cyclodextrin (β-CD). Results of a fluorescence spectroscopic examination of the β-CD-NFW system are presented. It was found that NFW forms a 1:1 inclusion complex with β-CD with an association constant of 2540 ± 380 M<sup>-1</sup>. The included NFW fluorescent state is protected by the β-CD cavity from a range of water-based quenchers (neutral, anionic and cationic). Quenching proceeds near the diffusion-controlled limit in water for the quenchers tested with the exception of the dicationic MV. MV is an extremely efficient quencher of NFW fluorescence with a nominal K<sub>SV</sub> ~ 5.0x10<sup>3</sup> M<sup>-1</sup> in water alone, corresponding to a nominal k<sub>q</sub> of ~ 4x10<sup>12</sup> M<sup>-1</sup>s<sup>-1</sup>, which exceeds the diffusion-controlled limit in this solvent. The quenching efficiency of MV is strongly suppressed in the presence of 10 mM β-CD (K<sub>SV</sub> = 105 ± 12 M<sup>-1</sup>) and in the presence of NaCl (K<sub>SV</sub> = 106 ± 9 M<sup>-1</sup> at 0.5 M salt). In the absence of CD or salt, there is a strong contribution from static quenching in the MV system; the presence of these additives suppresses the static quenching. Various results suggest the static quenching is due to formation of a ground-state complex between the dianion NFW and the dication MV.