This document discusses basic exchange rate theories using the elasticities and absorption approaches. It introduces key concepts such as the Marshall-Lerner condition, elasticities of export and import demand, and the J-curve effect. The elasticities approach uses export and import functions to model the relationship between the real exchange rate and the current account balance. Under the Marshall-Lerner condition, a real exchange rate change can improve the current account balance if the sum of the elasticities is greater than one. The absorption approach extends this framework to include income effects.