Active antioxidant food packaging is a technology in which an active compound (an antioxidant substance) is added to the packaging system to protect the food product from oxidation reactions, being an alternative technology to the direct incorporation to the food. This raises some challenges and interesting questions that are explored in this chapter. Although the active ingredient is located in the packaging its action is effectively manifested in the food. Is this achieved by a passive process, via an active release into the food or a combination of both mechanisms? The specific polymer layer structure, the antioxidant and the food matrix combination need to be considered holistically. Thus, an understanding of the total process occurring in different systems and matching release kinetics to food antioxidant demand requires measurement of antioxidant activity in both food and packaging. Also, the antioxidant material can exert indirect protection of the food by interaction with the headspace. This chapter examines the history and concept of active packaging with specific reference to antioxidants and crucially answers the questions related to the effectiveness of this technology, describing the diverse methodologies to assess the antioxidant capacity of the packaging system.