Patients with amyotrophic lateral sclerosis (ALS) invariably develop respiratory muscle weakness and most die from pulmonary complications. There are numerous tests available to evaluate respiratory status in ALS and it is important to understand their various advantages and limitations. Forced vital capacity (FVC) is commonly used but can remain normal despite substantial inspiratory muscle weakness. Maximal pressures measured at the mouth are useful for excluding weakness if they are normal but are difficult to interpret if abnormal. Invasive testing, such as measurement of transdiaphragmatic pressure, provides an accurate measure of inspiratory strength but is not readily available and is not practical for serial measures. There are supportive respiratory techniques that have been shown to benefit patients with ALS. Clinicians should be familiar with these interventions, including mechanically assisted coughing, non-invasive ventilation and tracheostomy with mechanical ventilation. Observational studies have demonstrated improved survival and quality of life with noninvasive ventilation. Tracheostomy with long-term mechanical ventilation is not frequently used but can be an important component of care for ALS. This review describes an approach to respiratory evaluation and care of patients with ALS.