1-Periods are complex numbers defined by integrating algebraic differential forms over paths (on algebraic varieties) with algebraic end points. The set contains many interesting numbers like $log(2)$ or $\pi$ that have been studied intensely in transcendence theorem. By the linear version of the Period Conjecture (a theorem of Wüstholz and myself in this case), all relations between them are described in terms of 1-motives. In this expository talk, we will explain this result and give a couple of examples.