Portuguese Abstract: Derivativos sao operacao paradoxais. Aparentemente simples, podem ser complexas na implementacao. Sao de elevado risco, ate mesmo para os agentes economicos mais sofisticados. O vocabulo “derivativo” possui pouco conteudo juridico e, por isso, as suas varias especies precisam ser estudadas adequadamente. Ja as operacoes compromissadas, em alguns pontos, assemelham-se aos derivativos. Mas, em tese, sao diferentes. Este capitulo estudara, de maneira sucinta, os dois tipos de operacao de acordo com o direito brasileiro. English Abstract: Derivatives are paradoxical transactions. Apparently simple, they can be complex in implementation. They are of high risk, even for the most sophisticated economic agents. The word "derivative" has little legal content and, therefore, its various species need to be studied properly. Repurchase transactions, in some respects, are similar to derivatives. But in theory, they are different. This chapter will briefly study the two types of transactions under Brazilian law.