1. Carbon dioxide (CO2): This is the primary source of carbon for the cycle, and it enters the cycle from the atmosphere.

2. ATP: This molecule provides the energy needed for the reactions in the Calvin cycle. It is produced during the light-dependent reactions of photosynthesis.

3. NADPH: This molecule provides the reducing power necessary to convert carbon dioxide into sugars. It is also produced during the light-dependent reactions of photosynthesis.

These three molecules are essential for the Calvin cycle to function and produce glucose, the main product of photosynthesis.