The truth belongs to no one. Through history, it always had diverse faces. Since antiquity many have struggled to define it… But over time, the truth has imposed itself as the horizon of any reasoned debate… Indeed, there is no possibility of progress in sciences without concern for accuracy and truth, no living democracy if its fundaments are built on lies, no relationship which is excepted to last without such a requirement, no proclamation of faith which is possible without being reconciled with reason, no press publication which is credible without an aspiration for objectivity. « Facts, only facts » are at the core of the journalistic ethic. Today, in most places, alternative truths are trying to be established in politics, economy or on a spiritual level. They are fed by relativism which is expanding all around, along with the overrating plurality of interpretation. Post-truth is constantly extending its authority and its ascendancy which makes debates increasingly complicated. Therefore, it is a critical challenge for all citizens including us, Christians, to be firmly at the service of truth.