Describes an integrated process for preparing 1,2-dichloroethylenes. In the described process organic feed material, e.g., C.sub.2-C.sub.4 aliphatic hydrocarbons and/or chlorinated derivatives of such aliphatic hydrocarbons, is introduced into a first reaction zone 10, e.g., a chlorination zone such as an oxychlorination zone, or a thermal cracking zone; first product effluent from the first reaction zone is forwarded to a second reaction zone 9; trichloroethane is introduced into the second reaction zone and into heat exchange contact with the first product effluent from the first reaction zone, which has a heat content sufficient to cause thermal dehydrochlorination of trichloroethane in the second reaction zone; and second product effluent is removed from the second reaction zone. 1,2-dichloroethylene is recovered by conventional distillation recovery methods from the second product effluent.