A discussion of cognates in second language teaching, particularly in English as a Second Language (ESL), looks at reasons and methods for teaching both true and false cognates ("friends"). A definition of cognates is offered, and a distinction is made between a cognate and a borrowed word, with examples from several languages. Textbooks' treatment of cognates is examined, and some problems arising from overemphasis on use of true cognates are noted, including potential for stilted language use and the danger of adopting false cognates. It is recommended that the teaching of false cognates be included in ESL instruction, to promote vocabulary development. Techniques include the teacher's development and incorporation into instruction of a collection of false cognates, using standard language exercises and games for identifying false cognates. Examples are offered. Contains six references. (MSE)