Hypovitaminosis D, a frequent condition in adults, is accompanied by adverse skeletal and non-skeletal events. The objective of the present article was to propose an update on the indications and use of vitamin D testing and supplementation in adults. Among healthy middle-aged adults, the serum 25-hydroxyvitamin D (25(OH)D) target concentration is 50 nmol/L. Natural intakes (sun exposure and diet) are sufficient, and there is no indication for systematic blood test or supplementation. In middle-aged adults who are either sick or dependent or frail, natural intakes are generally insufficient but should be encouraged. In this population, the loading phase of the supplementation targets a 25(OH)D concentration of 75 nmol/L, and the pattern of supplementation (200,000 to 400,000 IU orally over 2 months) depends on the measure of circulating 25(OH)D (which is not reimbursed outside the scope defined by the French national authority for health). In adults over 65 years of age, the loading phase of the supplementation should be systematic and targets a concentration of 75 nmol/L (pattern of 300,000 IU orally over 3 months). Regardless of age, the loading phase should be followed by a long-term maintenance phase of supplementation to maintain the 25(OH)D concentration above the target. A measure of serum 25(OH)D is useful after 9 months of supplementation to adjust the frequency or dosage of supplements if necessary.