The invention comprises urea and thiourea derivatives of the formula <FORM:0973352/C1/1> in which Ar is a phenyl ring, Q is oxygen or sulphur, R1 is hydrogen or a hydroxy group or an alkoxy group of less than 5 carbon atoms or, when Q is sulphur, is an alkyl group, R2 is hydrogen or an alkyl or alkoxy group of less than 5 carbon atoms and R3 is an alkyl group of less than 5 carbon atoms, at least one of R1 and R2 being an alkoxy group and/or R1 being a hydroxy group and the total number of carbon atoms in R2 and R3 being less than 6. When Q is sulphur, or when Q is oxygen and R1 is a hydroxy or alkoxy group, the ring Ar may be unsubstituted or substituted with up to three substituents, one of which is a halogen atom, a nitro group or an alkyl or alkoxy group of less than 5 carbon atoms, the other substituents, if any, being halogen atoms and/or methyl groups. When Q is oxygen and R1 is hydrogen, the ring Ar may be substituted (a) with one chlorine atom and a nitro group or (b) with three chlorine atoms, in which event R2 should be an alkoxy group of 2-4 carbon atoms. In any event the ring Ar must have a free 2-position. The compounds in which R1 is a hydroxy group may be prepared by reacting phenylhydroxylamine or a suitably substituted phenylhydroxylamine with a suitable carbamyl chloride or thiocarbamyl chloride or with a suitable isocyanate or isothiocyanate. Compounds in which R1 is an alkoxy group may be prepared by alkylating compounds in which R1 is a hydroxy group or by reacting N-alkoxyanilines with aliphatic amines or with alkyl-substituted hydroxylamines. Compounds in which R1 is hydrogen may be prepared by reacting an appropriate phenylisocyanate or phenylisothiocyanate with an N-alkyl-O-alkylhydroxylamine. Examples are given in which (1) 3, 4-dichlorophenylhydroxylamine and dimethylcarbamyl chloride yield 3-(3, 4-dichlorophenyl)-3-hydroxy-1, 1-dimethylurea, (2) p-chlorophenylhydroxylamine and methyl isocyanate yield 3-(p-chlorophenyl)-3-hydroxy-1-methylurea, (3) 3, 4-dichlorophenylisothiocyanate and N, O-dimethylhydroxylamine yield 3-(3, 4-dichlorophenyl) - 1 - methoxy -1- methylthiourea; compounds similarly obtainable are 3-(m-chlorophenyl)-1-methox-1-methylthiourea, 3-(3, 4-dichlorophenyl)-3-methoxy-1-methyl-thiourea, 3-(o-chlorophenyl)-3-butoxy-1-methylthiourea and 3- (3-chloro-4-nitrophenyl) -1- methyl-1-methoxy-thiourea; (4) N-methoxy-3, 4-dichloraniline and dimethylthiocarbamyl chloride yield 3-(3, 4-dichlorophenyl)-3-methoxy-1, 1-dimethylthiourea; 3-(3, 4-dichlorophenyl)-3-methoxy-1-butyl - 1 - methylthiourea is similarly obtainable; (5) N-methyl-3, 4-dichloraniline is treated with thiophosgene in the presence of triethylamine, and the product is treated with N-methyl-O-ethylhydroxylamine; 3-(3, 4-dichlorophenyl)-1, 3-dimethyl-1-ethoxythiourea is obtained; 3-(3, 4-dichlorophenyl)-1, 3-dimethyl-1-methoxythiourea and 3-(3, 4-dichlorophenyl)-3-ethyl-1-methoxy-1-methylthiourea are similarly obtainable; (6) N-ethoxy-3, 4-dichloraniline and N, O-dimethylhydroxylamine yield 3-(3, 4-dichlorophenyl)-3-ethoxy-1-methoxy-1-methylthiourea; (7) N-ethoxy-3, 4-dichloraniline and dimethylamine yield 3-(3, 4-dichlorophenyl)-3-ethoxy-1, 1-dimethylthiourea; (8) 3-nitro-4-chloro-phenylisocyanate and N, O-dimethylhydroxylamine yield 3-(3-nitro-4-chlorophenyl)-1-methyl - 1 -methoxyurea; (8) 6-chloro-4-nitrophenylisocyanate and N, O-dimethylhydroxylamine yield 3-(6-chloro-4-nitrophenyl)-1-methyl-1-methoxyurea. Other specified products include 3-phenyl-3-hydroxy-1-methylurea, 3-phenyl-3-hydroxy-1, 1-dimethylurea, 3-phenyl-3-hydroxy-1-butyl-1-methylurea, 3-(3-bromo-4-butoxyphenol)-3-hydroxy-1, 1-dimethylurea, 3 - (p-fluorophenyl) -3- hydroxy -1- methyl-1-propylurea, 3-phenyl-3-methoxy - 1 - methylurea, 3-phenyl-3-methoxy-1, 1-dimethylurea, 3-(p-bromophenyl)-3-ethoxy-1, 1-dimethylurea, 3-(p-fluorophenyl)-3-ethoxy-1-methoxy - 1 - methylurea and 3-phenyl-3-methoxy-1, 1-dimethylthiourea. The products are useful as herbicides. Specification 973,353 is referred to.ALSO:As components of herbicidal compositions, use is made of urea and thiourea derivatives of the formula <FORM:0973352/A5-A6/1> in which Ar is a phenyl ring, Q is oxygen or sulphur, R1 is hydrogen or a hydroxy group or an alkoxy group of less than 5 carbon atoms or, when Q is sulphur, is an alkyl group, R2 is hydrogen or an alkyl or alkoxy group of less than 5 carbon atoms and R3 is an alkyl group of less than 5 carbon atoms, at least one of R1 and R2 being an alkoxy group and/or R1 being a hydroxy group and the total number of carbon atoms in R2 and R3 being less than 6 (see Division C2). When Q is sulphur, or when Q is oxygen and R1 is a hydroxy or alkoxy group, the ring Ar may be unsubstituted or substituted with up to three substituents, one of which is a halogen atom, a nitro group or an alkyl or alkoxy group of less than 5 carbon atoms, the other substituents, if any, being halogen atoms and/or methyl groups. When Q is oxygen and R1 is hydrogen, the ring Ar may be substituted (a) with one chlorine atom and a nitro group or (b) with three chlorine atoms, in which event R2 should be an alkoxy group of 2-4 carbon atoms, In any event the ring Ar must have a free 2-position. Specified products include 3-(3,4-dichlorophenyl) - 3 - hydroxy - 1,1 - dimethylurea, 3 - (p - chlorophenyl) - 3 - hydroxy - 1 - methylurea, 3 - (3,4 - dichlorophenyl) - 1 - methoxy - 1 - methylthiourea, 3 - (m - chlorophenyl) - 1 - methoxy - 1 - methylthiourea, 3 - (3,4 - dichlorophenyl) - 3 - methoxy - 1 - methylthiourea, 3 - (o - chlorophenyl) - 3 - butoxy - 1 - methylthiourea, 3 - (3 - chloro - 4 - nitrophenyl)-1 - methyl - 1 - methoxythiourea, 3 - (3 - chloro - 4 - isopropylphenyl) - 1 - methoxy - 1 - methylthiourea, 3 - (p - bromophenyl) - 1 - methoxy - 1 - methylthiourea, 3 - (3,4 - dichlorophenyl) - 3 - methoxy - 1,1 - dimethylthiourea, 3 - (3,4 - dichlorophenyl) - 3 - methoxy - 1 - butyl - 1 - methylthiourea, 3 - (3,4 - dichlorophenyl) - 3 - ethoxy - 1 - methoxy - 1 - methylthiourea, 3 - (3,4 - dichlorophenyl) - 3 - ethoxy - 1,1 - dimethylthiourea, 3 - (6 - chloro - 4 - nitrophenyl)-1 - methyl - 1 - methoxyurea, 3 - phenyl - 3 - hydroxy - 1 - methylurea, 3 - phenyl - 3 - hydroxy - 1,1 - dimethylurea, 3 - phenyl - 3 - hydroxy - 1 - butyl - 1 - methylurea, 3 - (3 - bromo - 4 - butoxyphenyl) - 3 - hydroxy - 1,1 - dimethylurea, 3 - (p - fluorophenyl) - 3 - hydroxy - 1 - methyl - 1 - propylurea, 3 - phenyl - 3 - methoxy - 1 - methylurea, 3 - phenyl - 3 - methoxy - 1,1 - dimethylurea, 3 - (p - bromophenyl) - 3 - ethoxy - 1,1 - dimethylurea, 3 - (p - fluorophenyl) - 3 - ethoxy - 1 - methoxy - 1 - methylurea and 3 - phenyl - 3 - methoxy - 1,1 - dimethylthiourea. The products may be formulated as solid or liquid compositions with the addition of solid or liquid compositions with the addition of solid or liquid diluents, a number of which are specified. The compositions may also contain surface-active agents, a number of which are specified. Other herbicides, insecticides, fungicides and fertilizers may also be included in the compositions. The p compositions may be used for the treatment of growing weeds or they may be applied to the soil in areas where a growth of weeds might otherwise have been expected. Examples of herbicidal compositions are given. Specification 973,353 is referred to.