The decline of employment in the European agriculture sector increases the need of EU and non-EU seasonal workers at peaks of planting and harvesting activities. EU citizens’ freedom and right to work across the Union allows the proper functioning of the market economy by providing labour where and when it is needed. Still, after 30 years of the single market, once seasonal workers arrive at their destination, they are subject to fragmented, often localised, employment arrangements and rules. Non-EU seasonal workers follow different mobilisation mechanisms, but end up in the same fragmented situations. In this context, characterisation and quantification of seasonal work in the agriculture and food sectors is a challenge. Due to the lack of sufficient law enforcement capacity at the territorial level by social (e.g., trade unions) and government (e.g., labour inspection units) actors, seasonal workers’ rights in terms of social protection and decent working and living conditions can be violated by unethical employers, intermediaries, or even crime organisations. This study collects evidence on data/information gaps; draws insights from Italy, Spain and the Netherlands; highlights problems and makes suggestions to improve the working and living conditions as well as the protection of seasonal agri-food workers in Europe.