The invention comprises substituted 2-(21-hydroxyphenyl) benztriazoles of the general formula <FORM:0991630/C2/1> wherein X represents a divalent bridging member chose from -O-, -S-, <FORM:0991630/C2/2> -SO2O-, <FORM:0991630/C2/3> , -COO- or -SO2-, wherein Z represents hydrogen or an alkyl radical and the X moiety is bound to the nucleus by O, S or C; Y represents a divalent aliphatic, cycloaliphatic, monocyclic araliphatic or monocyclic aromatic radical in which any hetero atoms are separated by at least two carbon atoms from one another or from hetero atoms contained in X or W; W represents CN-, -CONR1R11 or -COOR where R, R1 and R11 independently represent hydrogen or alkyl, cycloalkyl, monocyclic aralkyl or monocyclic aryl radicals: n is 1 or 2; and m is 1 or 2 and wherein the nucleus may be substituted in the 4, 5 and 6 positions by alkyl, alkoxy, carboxy, carboxylic acid acid ester or amide, sulphonic acid amide, alkylsulphonyl groups or halogens, and in the 31, 41 and 51 positions by alkyl, cycloalkyl, aralkyl, aryl and alkoxy groups or halogen and wherein the grouping <FORM:0991630/C2/4> is bound to at least one of the positions 4, 5, 6, 31, 41 and 51 with the proviso that if the group is bound at the 31 position it does not spontaneously form a lactone ring.  These compounds may be prepared from an azo dyestuff (see Division C4) of the formula <FORM:0991630/C2/5> wherein Q represents a nitro or primary amino group and R represents hydrogen, an alkyl, aralkyl or acyl group, by reduction when Q is nitro, or oxidation, when Q is amino, and subsequent liberation of the etherified or esterified 21-hydroxy group. Other methods of preparation are (1) by reacting, e.g. by heating in an organic solvent in the presence of an agent which splits off the acid (e.g. an alkali metal salt of a fatty acid), a 61 unsubstituted-2-(21-hydroxyphenyl) benztriazole compound containing at least one other etherifiable hydroxy and/or mercapto group in the nucleus with an organic compound containing possibly esterified carboxyl groups and mobile halogen, e.g. chloroacetic acid; (2) by reacting, e.g. by heating, advantageously in an organic solvent, in the presence of a polymerization inhibitor, a 61 - unsubstituted - 2 - (21 - hydroxyphenyl) benztriazole containing at least one other etherifiable hydroxy and/or mercapto group in the nucleus with an organic compound which contains possibly esterified carboxyl groups or which liberates such groups, e.g. acrylonitrile; (3) by reacting, e.g. by heating in an organic solvent in the presence of an acid binding agent and salts of weak acids, a 2-(21-hydroxyphenyl) benztriazole compound having a substituent containing mobile halogen, e.g. carboxylic acid or sulphonic acid chloride group, with a compound containing a condensable group, e.g. amino or hydroxyl .group, and at least one possibly modified carboxyl group; and (4) by reacting, e.g. by heating in an organic solvent possibly in the presence of catalysts, a 2 - (21 - hydroxyphenyl)benztriazole compound having a substituent containing at least one group capable of addition, e.g. activated vinyl or vinylidene groups, with a compound containing mobile hydrogen, e.g. in hydroxyl, mercapto or amino groups, and at least one possibly modified carboxyl group. Several examples of the preparation and use of the compounds of the invention are given (see Divisions C3, C4 and G2).  Reference has been directed by the Comptroller to Specification 878,362.ALSO:Synthetic and natural polymers are stabilized against light by the incorporation, usually as 0.001 to 5% by weight, therein of substituted 2 - (21 - hydroxyphenyl) benztriazoles of the general formula <FORM:0991630/C3/1> wherein X represents a divalent bridging member chosen from -O-, -S-, <FORM:0991630/C3/2> , -SO2O-, <FORM:0991630/C3/3> , -COO- or -SO2-, wherein Z represents hydrogen or an alkyl radical and the X group is bound to the nucleus by O, S or C; Y represents a divalent aliphatic, cycloaliphatic, monocyclic araliphatic or monocyclic aromatic radical in which any hetero atoms are separated by at least two carbon atoms from one another or from hetero atoms contained in X or W; W represents CN-, -CONR1R11 or -COOR, where R, R1 and R11 independently represent hydrogen or alkyl, cycloalkyl, monocyclic aralkyl or monocyclic aryl radicals; n is 1 or 2; and m is 1 or 2 and wherein the nucleus may be substituted in the 4, 5 and 6 positions by alkyl, alkoxy, carboxy, carboxylic acid ester or amide, sulphonic acid amide, alkylsulphonyl groups or halogens, and in the 31, 41 and 51 positions by alkyl, cycloalkyl, aralkyl, aryl and alkoxy groups or halogen and wherein the grouping (x)n- 1-Y-W is bound to at least one of the positions 4, 5, 6, 31, 41 and 51 with the proviso that if the group is bound at the 31 position it does not spontaneously form a lactone ring.  Specified polymers are the polymers and copolymers of ethylenically unsubstituted monomers, polyacrylic compounds, polyesters, polyamides, polyester resins, cellulose, cellulose esters and ethers, and proteins.  Reference has been directed by the Comptroller to Specification 878,362.ALSO:Lacquers used to protect light-sensitive materials from light contain at least one substituted 2 - (21 - hydroxyphenyl) benztriazole of the general formula <FORM:0991630/C4-C5/1> <FORM:0991630/C4-C5/2> wherein X represents a divalent bridging member chosen from -O-, -S-, <FORM:0991630/C4-C5/3> -COO- or -SO2-, wherein Z represents hydrogen or alkyl radical and the X moiety is bound to the nucleus by O, S or C; Y represents a divalent aliphatic, cycloaliphatic, monocyclic araliphatic or monocyclic aromatic radical in which any hetero atoms are separated by at least two carbon atoms from one another or from hetero atoms contained in X or W; W represents CN-, CONR1 R11 or -COOR, where R, R1 and R11 independently represent hydrogen or alkyl, cycloalkyl, monocyclic aralkyl or monocyclic aryl radicals; n is 1 or 2; and m is 1 or 2 and wherein the nucleus may be substituted in the 4, 5 and 6 positions by alkyl, alkoxy, carboxy, carboxylic acid ester or amide, sulphonic acid amide, alkylsulphonyl groups or halogens, and in the 31, 41 and 51 positions by alkyl, cycloalkyl, aralkyl, aryl and alkoxy groups or halogen and wherein the grouping <FORM:0991630/C4-C5/4> is bound to at least one of the positions 4, 5, 6, 31, 41 and 51 with the proviso that if the group is bound at the 31 position it does not spontaneously form a lactone ring. Starting materials for one of the methods of preparing compounds of the above formula are azo-dyes of the general formula <FORM:0991630/C4-C5/5> wherein #j represents a nitro or primary amino group and R represents hydrogen, an alkyl, aralkyl or acyl group. Said dyes may be prepared by diazo coupling of (a) nitrobenzenediazonium compounds with 3 unsubstituted phenols (#j = nitro) or (b) 2-hydroxy-, alkoxyor acyloxy-benzene-diazonium compounds with aminobenzene (#j = primary amino).  Reference has been directed by the Comptroller to Specification 878,362.