Stir together all three ingredients in a small saucepan. Bring to a boil over medium heat.
When the first bubbles appear, reduce heat to medium-low and gently simmer 4 minutes. Remove from heat, and let mixture cool for 30 minutes. Strain mixture to remove raspberry seeds.
Carefully pour into a glass jar or another air-tight container. Store in the refrigerator. Keeps up to 2 weeks when kept in the refrigerator.
Note
Raspberry simple syrup is perfect for use in iced teas, cocktails, mocktails, or on top of pancakes and waffles.