Flavor is the sensory impression of a food and is determined mainly by the chemical senses of smell and taste. In this chapter, the focus will be on the chemicals that produce aroma, rather than taste-related responses, and how these aroma compounds are generated. It is the aroma of food that allows us to distinguish between many different types of food and also to perceive the subtle nuances between similar products. In addition, the aroma from stale, rancid, or putrefying food is an indication that the food is not in its optimum condition and, in extreme cases, may not be safe for consumption. This chapter is divided into several sections: the ˜rst section describes how we can characterize aroma compounds, the second section describes the aroma compounds found in vegetables and fruits, and the following sections describe the aromas that are thermally or biochemically generated.