Three cyanate esters containing phosphorus are synthesized in good overall yields starting from bromoanisoles. Di- and tricyanates with meta configuration are most stable while para is less so. The para dicyanate ester isomer is particularly affected by water from the atmosphere. The meta dicyanate ester 2 has good thermal properties with glass transition at 268 degrees C and char yield of 65% in air at 600 degrees C. All three phosphorus-containing cyanate esters are low flammability in an open flame. They make highly combustible cyanate esters resins less flammable simply by blending. Mixing 10 wt% dicyanate ester 2 into bisphenol A or E dicyanate esters makes them rate V-0. Published 2018.(dagger) J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1100-1110