The dew point is the temperature to which a parcel of air must cool, assuming constant pressure and water-vapor content, to reach saturation.
The dew point will always be lower than the wet bulb temperature, which will always be lower than the dry bulb temperature. The only time this does not hold true is when saturation occurs, during which time all three values are equal.
Source: National Wildfire Coordinating Group. 2012. Glossary of Wildland Fire Terminology. PMS 205. Accessed on 9 September 2013. Available at http://www.nwcg.gov