Ethylene has a worldwide production of ∼ 117 million ton/yr in about 275 plants. A discussion covers alternative processes, with emphasis on the reactor section of the process; feedstocks for thermal cracking, e..g, ethane, LPG, naphtha, gas condensates, and gas oil; the ability to create a near-optimum reaction path from hydrocarbon feed to ethylene; critical reactor aspects; dehydrogenation, direct and indirect heating processes; an engineering point of view of thermal cracking by direct heating with gasses; environmental concerns; and future process routes for ethylene. This is an abstract of a paper presented at the AIChE Spring Meeting - 19th Ethylene Producers Conference (Houston, TX 4/22-27/2007).