Resumo: System L is a linear version of Godel's System T , where the Lambda-calculus is replaced with a linear calculus; or alternatively a linear Lambda-calculus enriched with some constructs  including an iterator. There is thus at the same time in this system a lot of freedom in reduction and a lot of information about resources, which makes it an ideal framework to start a fresh attempt at studying reduction strategies in lambda-calculi. In particular, we show that call-by-need, the standard strategy of functional languages, can be defined directly and effectively in System L, and can be shown to be minimal among weak strategies.