Antimicrobial (AM) films containing naturally-derived AM agents, thymol or carvacrol, were developed. These agents were incorporated into a low-density polyethylene (LDPE) substrate using the techniques of both compression moulding and extrusion film blowing. Different film formulations containing additive polymers, ethylene vinyl acetate (EVA) and polyethylene glycol (PEG), were investigated for their potential to enhance the retention and to control the release of the AM agents from the films. The physical and mechanical properties of the films were evaluated in order to assess the effect that the addition of AM agent has on the ultimate properties of the film. The extruded films were also studied for AM agent release and retention during storage. Films were tested for AM activity in-vitro enabling the optimum concentrations for AM activity to be obtained and the effect of AM films on the bacterial inhibition in liquid media to be successfully modelled. The effects of combined AM systems in LDPE/EVA-based films were also studied. Having identified the AM activity in laboratory media, the films were then used to package Cheddar cheese in order to assess the usefulness of AM films in the enhancement of food preservation. The AM films had a positive effect on the microbial and physio-chemical attributes of Cheddar cheese under actual storage conditions. The addition of higher concentrations of AM agents clearly imparted a noticeable odour to Cheddar cheese during storage. The shelf life extension of Cheddar cheese by AM films was affected by the type and concentration of the AM agent.