A food quality sensor is a device that responds to some property associated with food quality and transforms the response into a signal (1). This signal may provide direct information about the quality factor to be measured or may have a known relationship to the quality factor. On-line food quality sensors operate directly in the process stream, giving a real-time signal that relates to the quality factor in question. Therefore, an online sensor has the advantage of giving an immediate measurement allowing processes to be adjusted if necessary (1). This thesis is based on 3 projects describing the design and development of on-line food quality sensor systems for specific food applications as`outlined below: Project 1: Development of an autonomous, wireless pH and temperature sensing system for monitoring pig meat quality. Project 2: Development of a web-based wireless temperature sensing system for the fishing industry. Project 3: Development of on-package sensors to detect shellfish. Projects 1 & 2 describe pH and temperature sensors which are coupled with wireless communications to create autonomous, wireless sensing devices capable of delivering data in real-time to a remote PC where the data can be analysed or automatically uploaded onto the internet via specifically designed web-enabled software. Project 3 focuses on the development of pH sensitive polymer membranes that change colour in response to spoilage volatiles released by shellfish packed in sealed containers. Field trials performed with the aid of Irish food industries and collaborating Irish research institutes played a major role in obtaining the results for each of the mentioned projects. These include the Department of Food and Nutritional Sciences, University College Cork; Galtee Meats, Mitchelstown, Co. Cork; Bord Iascaigh Mhara (BIM) coastal staff and Errigal Iasc, Carrick, Co. Donegal. The following thesis gives a detailed account of the recent challenges faced by the Irish food sector including the detection of poor quality pig meat, traceability and temperature control within the fishing industry and methods to evaluate seafood spoilage. The research activities carried out to overcome such challenges are discussed including the potential impact on the Irish food industry.