This is a randomized, crossover trial for patient with ALS and mild respiratory involvement. Patients with forced vital capacity above 60% of the predicted value can join. Patients will be assigned to either start using non-invasive ventilation at night or continue their usual care. After three months, patients will switch over to the other treatment group. For example, a patient who was initially assigned to continue their usual care would begin using non-invasive ventilation after three months.