MIT economist Arnaud Costinot walks through seven questions about tariffs, combining trade theory with data from recent history. He starts with what is always bad about tariffs and what is potentially good, then works through when a country might justifiably use them and how to judge whether a specific set of tariffs helps or hurts. Later segments turn to evidence: the impact of the 2018 to 2019 US-China trade war, whether global tariff structures are actually unfair to the United States, and what makes trade wars genuinely damaging beyond the tariffs themselves. Delivered as part of MIT's January IAP short-course series (RES.14-004), the talk runs just over an hour and moves briskly from one question to the next, using standard trade models alongside real trade-war data to separate rhetoric about tariffs from what economists can actually show.